1 00:00:00,800 --> 00:00:02,440 In the Middle East 2 00:00:02,600 --> 00:00:07,080 between the Red Sea and the Dead Sea is Petra. 3 00:00:07,240 --> 00:00:10,320 A city nestled in the middle of the Jordanian desert, 4 00:00:10,480 --> 00:00:11,880 in a vast rocky massif. 5 00:00:12,040 --> 00:00:13,720 Built over 2000 years ago 6 00:00:13,880 --> 00:00:17,520 by a nomadic Arab population called the Nabataeans, 7 00:00:17,680 --> 00:00:20,560 many people consider it the eighth wonder of the world. 8 00:00:20,720 --> 00:00:23,080 It is an incredible place. 9 00:00:23,240 --> 00:00:25,560 The colours of Petra are just amazing. 10 00:00:25,720 --> 00:00:27,680 You feel you are not on this planet. 11 00:00:28,760 --> 00:00:32,080 Petra is known for its huge facades, carved out of the rock, 12 00:00:32,240 --> 00:00:34,800 which are often used as scenery for films. 13 00:00:34,960 --> 00:00:36,600 But taking to the skies, 14 00:00:36,760 --> 00:00:40,120 we discover an archaeological site stretching 260 square kilometres 15 00:00:40,280 --> 00:00:42,640 with over 850 remains. 16 00:00:42,800 --> 00:00:46,560 An immense city which still has many secrets to uncover. 17 00:00:46,720 --> 00:00:49,040 It's like a puzzle, a huge puzzle. 18 00:00:49,200 --> 00:00:52,320 We only have a glimpse of this glorious city. 19 00:00:52,480 --> 00:00:55,560 This city, forgotten for centuries, 20 00:00:55,720 --> 00:00:58,960 was rediscovered by a Swiss explorer 200 years ago. 21 00:00:59,120 --> 00:01:03,320 Today, archaeologists are still trying to complete its story 22 00:01:03,480 --> 00:01:05,960 and unravel the mysteries that elude them. 23 00:01:06,120 --> 00:01:08,480 So we need some good pictures of this area. 24 00:01:09,480 --> 00:01:11,760 With the help of the most modern scientific tools, 25 00:01:11,920 --> 00:01:14,480 they can probe the work of ancient builders. 26 00:01:14,640 --> 00:01:16,320 These technologies are giving us 27 00:01:16,480 --> 00:01:18,560 real insight into the building methods. 28 00:01:18,720 --> 00:01:21,280 By examining Petra from different perspectives, 29 00:01:21,440 --> 00:01:24,280 from the infinitely big to the infinitely small, 30 00:01:24,440 --> 00:01:28,800 experts can detect details that are invisible to the human eye. 31 00:01:28,960 --> 00:01:33,800 It's very exciting. We're almost on the telephone to the past. 32 00:01:33,960 --> 00:01:35,880 Thanks to digital tools, 33 00:01:36,040 --> 00:01:39,520 the luxurious structures from Petra's golden age are brought back to life. 34 00:01:39,680 --> 00:01:43,120 This mythical city, which was at its peak in the 1st century B.C. 35 00:01:43,280 --> 00:01:45,760 can finally reveal its true splendour. 36 00:01:45,920 --> 00:01:49,320 Petra demonstrates opulence. 37 00:01:49,480 --> 00:01:54,760 These cascading fountains and pools. It's almost as if it's showing off. 38 00:01:54,920 --> 00:01:57,160 A Las Vegas of its time. 39 00:01:58,520 --> 00:02:01,640 We will unlock the secrets of this sprawling desert city 40 00:02:01,800 --> 00:02:04,480 by examining its spectacular structures, 41 00:02:04,640 --> 00:02:08,280 starting with its most famous monument, Al-Khazneh. 42 00:02:08,440 --> 00:02:14,240 It is so dramatic, because it's sculpted out of the rock itself. 43 00:02:15,320 --> 00:02:19,280 What techniques did the Nabataeans, a population of nomadic traders, 44 00:02:19,440 --> 00:02:22,880 use to build such tall structures without modern tools? 45 00:02:23,040 --> 00:02:25,120 How did their masons transform 46 00:02:25,280 --> 00:02:28,240 this raw stone into an architectural diamond? 47 00:02:29,200 --> 00:02:32,480 And how did they find water in the middle of the desert 48 00:02:32,640 --> 00:02:36,240 and create one of Antiquity's most advanced hydraulic systems? 49 00:02:36,400 --> 00:02:39,240 It had water and that is Petra's secret. 50 00:02:39,400 --> 00:02:43,200 The main ingenious engineering of the Nabataeans 51 00:02:43,360 --> 00:02:45,960 was their hydraulic engineering. 52 00:02:46,560 --> 00:02:49,160 History, science, construction - 53 00:02:49,320 --> 00:02:51,560 examined like never before. 54 00:02:51,720 --> 00:02:55,200 Petra reveals its secrets on every scale. 55 00:03:06,240 --> 00:03:09,360 To understand Petra, you first have to understand the secrets 56 00:03:09,520 --> 00:03:12,160 of this fascinating city's construction. 57 00:03:12,320 --> 00:03:14,400 It was built in the 1st century B.C. 58 00:03:14,560 --> 00:03:17,200 by a population of nomads, the Nabataeans. 59 00:03:19,800 --> 00:03:23,160 At the time, and still today, each visitor would enter 60 00:03:23,320 --> 00:03:26,800 by following this astonishing and winding natural passage, 61 00:03:26,960 --> 00:03:28,800 known as the Siq. 62 00:03:28,960 --> 00:03:32,600 1200 metres long and, in places, less than 3 metres wide, 63 00:03:32,760 --> 00:03:36,520 it leads to this breath-taking building, Al-Khazneh. 64 00:03:47,880 --> 00:03:50,360 The outside was meant to be seen. 65 00:03:51,360 --> 00:03:54,640 This was...to woo. 66 00:03:57,320 --> 00:04:00,880 For archaeological experts, this monument is a true enigma. 67 00:04:01,280 --> 00:04:05,000 Now, thanks to new technology, they can unlock its secrets. 68 00:04:05,880 --> 00:04:09,720 It's just mind boggling, the skill that went into it. 69 00:04:09,880 --> 00:04:15,040 The lines are so clean, the reliefs are so beautiful. 70 00:04:15,200 --> 00:04:17,640 And there's just no mistakes. 71 00:04:18,880 --> 00:04:22,080 If you look at the detailed carvings, 72 00:04:22,240 --> 00:04:26,800 not only of the figures, but the decorations. 73 00:04:26,960 --> 00:04:28,160 Perfect! 74 00:04:28,320 --> 00:04:32,760 This incredible lavishly decorated temple is about 39 metres high, 75 00:04:32,920 --> 00:04:35,680 the equivalent of a 12-storey building. 76 00:04:35,840 --> 00:04:38,440 But how did the Nabataens carve a structure 77 00:04:38,600 --> 00:04:42,080 which is as monumental as it is perfect, from solid rock? 78 00:04:42,240 --> 00:04:44,640 The interesting thing when we see the Khazneh 79 00:04:44,800 --> 00:04:46,800 is first obviously its scale. 80 00:04:46,960 --> 00:04:49,280 It's always been a mystery as to how 81 00:04:49,440 --> 00:04:54,840 they were able to construct these sculptures so high above the ground. 82 00:04:57,120 --> 00:05:01,840 In this arid desert, wood resources are practically non-existent. 83 00:05:02,000 --> 00:05:06,080 It is impossible to find sufficient planks to build scaffolding. 84 00:05:06,240 --> 00:05:10,400 So, how did the Nabataeans raise themselves 40 metres from the ground 85 00:05:10,560 --> 00:05:13,680 in order to sculpt Al-Khazneh? 86 00:05:15,120 --> 00:05:18,480 To solve this mystery, archaeologists today, 87 00:05:18,640 --> 00:05:20,680 combine traditional observation techniques 88 00:05:20,840 --> 00:05:22,920 with sophisticated technology 89 00:05:23,080 --> 00:05:26,880 revealing details that the human eye can't easily perceive. 90 00:05:27,040 --> 00:05:30,600 Qais Tweissi is the site's technical curator 91 00:05:30,760 --> 00:05:33,600 Thanks to this machine called a "total station", 92 00:05:33,760 --> 00:05:36,240 he can take precise measurements of the building. 93 00:05:36,400 --> 00:05:38,920 Then, he processes the data on a computer 94 00:05:39,080 --> 00:05:42,920 to build an extremely accurate 3D projection. 95 00:05:43,200 --> 00:05:48,960 Which gives us a very good accuracy, which is about 0.01 mm, 96 00:05:49,120 --> 00:05:51,680 which is very good for documentation. 97 00:05:53,560 --> 00:05:57,920 The 3D model lets experts examine the smallest details of the facade. 98 00:05:58,080 --> 00:05:59,440 But do any clues remain 99 00:05:59,600 --> 00:06:03,040 that could reveal the Nabataeans' construction techniques? 100 00:06:03,200 --> 00:06:06,200 Details like the remains of fastenings for scaffolding? 101 00:06:09,040 --> 00:06:11,160 The first feature which become apparent 102 00:06:11,320 --> 00:06:13,880 are notches on either side of the monument. 103 00:06:15,920 --> 00:06:18,600 Changing the scale, thanks to digital zoom, 104 00:06:18,760 --> 00:06:21,320 reveals the shape of these strange notches. 105 00:06:21,480 --> 00:06:24,080 They are deeper at the base than at the top. 106 00:06:26,160 --> 00:06:29,280 They appear to be shaped for a human foot. 107 00:06:30,400 --> 00:06:34,920 But did Nabataean builders use them to access the construction site? 108 00:06:46,680 --> 00:06:52,080 One of the theory for those foot holes is for climbing the monument 109 00:06:52,240 --> 00:06:54,720 looking for special finds like gold, 110 00:06:54,880 --> 00:06:59,320 and also for broking the figures of the monument. 111 00:06:59,480 --> 00:07:04,040 So these notches were hollowed out by raiders and not by the builders. 112 00:07:05,840 --> 00:07:09,720 Thanks to a careful examination of the facade and the digital model, 113 00:07:09,880 --> 00:07:13,640 archaeologists have also ruled out other false leads. 114 00:07:13,800 --> 00:07:15,640 For example, these small holes 115 00:07:15,800 --> 00:07:18,920 are not the remains of fastenings for scaffolding, 116 00:07:19,080 --> 00:07:21,280 they're bullet holes or marks from tools 117 00:07:21,440 --> 00:07:24,080 made long after the construction of Al-Khazneh. 118 00:07:24,240 --> 00:07:26,840 To solve the enigma of its construction, 119 00:07:27,000 --> 00:07:29,440 experts have had to find other clues. 120 00:07:31,840 --> 00:07:36,000 Thibaud Fournet is a French architect and engineer at the CNRS. 121 00:07:36,160 --> 00:07:39,360 He has been studying one particular cliff for several months, 122 00:07:39,520 --> 00:07:41,800 using a variety of techniques. 123 00:07:41,960 --> 00:07:46,000 This cliff is the site of a unique, partially carved building 124 00:07:46,160 --> 00:07:49,200 known as the "unfinished monument". 125 00:08:04,760 --> 00:08:08,960 The site allows Thibaud to analyse the ancient builders' work. 126 00:08:09,120 --> 00:08:13,640 This 4-column monument was intended to run down the side of the cliff. 127 00:08:13,800 --> 00:08:16,280 Only the upper parts have been carved. 128 00:08:16,440 --> 00:08:19,680 Which means that the stone-cutters started from the top. 129 00:08:19,840 --> 00:08:23,280 But how could they have worked on such a steep cliff? 130 00:08:26,520 --> 00:08:29,160 You can see this reddish part. Yes. 131 00:08:29,320 --> 00:08:32,560 I need on this part, good pictures from quite close. 132 00:08:32,720 --> 00:08:36,440 Today, Thibaud wants to observe architectural features 133 00:08:36,680 --> 00:08:38,440 at the top of the facade. 134 00:08:38,600 --> 00:08:40,320 Just like the Nabateans, 135 00:08:40,480 --> 00:08:44,040 he has also had to find a way to access the cliff. 136 00:08:45,800 --> 00:08:47,160 Thanks to this drone, 137 00:08:47,320 --> 00:08:50,320 the team can collect clues that were unattainable until now, 138 00:08:50,480 --> 00:08:53,360 in order to process them in 3D. 139 00:08:53,520 --> 00:08:55,840 These previously unseen images, 140 00:08:56,000 --> 00:08:58,600 alongside traditional observations made 20 years ago, 141 00:08:58,760 --> 00:09:01,560 allow archaeologists to piece together 142 00:09:01,720 --> 00:09:04,720 the secrets of the Nabataeans' construction techniques. 143 00:09:06,400 --> 00:09:08,320 To sculpt this kind of structure, 144 00:09:08,480 --> 00:09:11,520 ancient stone-carvers started by smoothing the rock, 145 00:09:11,680 --> 00:09:15,840 creating a flat wall which marked out the front of their building. 146 00:09:25,960 --> 00:09:27,720 On this blank canvas of rock, 147 00:09:27,880 --> 00:09:30,520 the Nabateans hollowed out small terraces 148 00:09:30,680 --> 00:09:34,080 which allowed them to sculpt the rock face in complete safety. 149 00:09:44,840 --> 00:09:47,000 After completing the upper parts, 150 00:09:47,160 --> 00:09:51,440 workers needed extreme attention to detail as they gradually descended, 151 00:09:51,600 --> 00:09:53,800 finishing with the foundations. 152 00:09:54,920 --> 00:09:57,840 The fact that they had to do the whole facade in one go 153 00:09:58,000 --> 00:10:03,120 with no chance to restart or to repair a mistake 154 00:10:03,280 --> 00:10:08,600 is something very courageous and a risk that nobody could bear today. 155 00:10:08,760 --> 00:10:11,960 In Petra, you need preciseness and engineering, 156 00:10:12,120 --> 00:10:14,120 that means if a mistake would go, 157 00:10:14,280 --> 00:10:16,400 that means the whole facade is destroyed. 158 00:10:17,280 --> 00:10:21,120 Researchers haven't found any plans or written records about Al-Khazneh, 159 00:10:21,280 --> 00:10:24,520 but they assume that the Nabataeans planned their construction 160 00:10:24,680 --> 00:10:26,320 to the smallest detail. 161 00:10:38,360 --> 00:10:41,480 At Al-Khazneh, the ancient builders erased 162 00:10:41,640 --> 00:10:44,600 all traces of their construction as they worked. 163 00:10:44,760 --> 00:10:46,280 But taking a step back, 164 00:10:46,440 --> 00:10:48,960 we can see evidence that this structure was also built 165 00:10:49,120 --> 00:10:51,400 using the inverted construction technique. 166 00:10:52,120 --> 00:10:54,280 To the right of the monument, these stairs, 167 00:10:54,440 --> 00:10:57,960 discovered at the same time as the site in the 19th century, 168 00:10:58,120 --> 00:11:01,440 allowed workers to access the construction site. 169 00:11:02,080 --> 00:11:03,960 But a mystery remains. 170 00:11:04,120 --> 00:11:06,360 How can this monumental facade stand, 171 00:11:06,520 --> 00:11:08,720 when it was impossible for the Nabataeans 172 00:11:08,880 --> 00:11:11,000 to test the strength of its foundations 173 00:11:11,160 --> 00:11:13,560 before they started building? 174 00:11:13,720 --> 00:11:16,680 The images taken by drone reveal an immense massif 175 00:11:16,840 --> 00:11:18,520 which overlooks Al-Khazneh. 176 00:11:18,680 --> 00:11:22,280 Hundreds of tons of rocks weigh down on the monument. 177 00:11:23,120 --> 00:11:27,240 How could the Nabataeans be sure that these structures wouldn't crumble 178 00:11:27,400 --> 00:11:29,560 underneath this immense weight? 179 00:11:29,720 --> 00:11:32,360 One of the principles of construction 180 00:11:32,520 --> 00:11:35,280 is that you have to transfer the load 181 00:11:35,440 --> 00:11:38,360 from its highest point down to the ground, 182 00:11:38,520 --> 00:11:42,560 and when you look at the sculpture, each of the elements, 183 00:11:42,720 --> 00:11:46,560 the weight is transferred down to the ground through the column. 184 00:11:46,720 --> 00:11:50,280 At first glance, the support element seems obvious. 185 00:11:50,440 --> 00:11:54,280 A monumental lintel held up by six immense columns, 186 00:11:54,440 --> 00:11:56,720 cut directly into the rock face. 187 00:11:56,880 --> 00:11:59,120 But appearances can be deceiving. 188 00:11:59,880 --> 00:12:01,840 On 19th century engravings, 189 00:12:02,000 --> 00:12:05,440 we discover that one of the load-bearing columns was broken. 190 00:12:05,600 --> 00:12:11,000 It wasn't repaired until the 1960s. Yet the building didn't collapse. 191 00:12:12,720 --> 00:12:16,520 The 3D model of the monument, built using data from the total station, 192 00:12:16,680 --> 00:12:19,360 reveals the solution to what holds up the structure. 193 00:12:20,280 --> 00:12:24,160 From the side, we realise that the lintel is built into the cliff. 194 00:12:24,320 --> 00:12:27,680 So are all of the columns, except for the two central ones. 195 00:12:28,440 --> 00:12:32,280 So it's the rock wall itself which is supporting most of the weight, 196 00:12:32,440 --> 00:12:36,120 and not the facade which is almost like an optical illusion. 197 00:12:38,360 --> 00:12:41,960 The interior of Al-Khazneh confirms this hypothesis. 198 00:12:42,120 --> 00:12:44,640 Usually it is closed to the public. 199 00:12:45,640 --> 00:12:50,120 But Qais Tweissi has special permission to explore inside. 200 00:12:50,280 --> 00:12:54,200 Surprisingly, the interior of Al-Khazneh is much less spectacular 201 00:12:54,360 --> 00:12:56,480 than the outside suggests. 202 00:12:56,640 --> 00:12:58,320 This looks from outside very huge, 203 00:12:58,480 --> 00:13:00,880 and from the interior, small chamber. 204 00:13:01,400 --> 00:13:05,840 One master chamber, ten metres high and undecorated 205 00:13:06,000 --> 00:13:08,600 leading to three much smaller rooms. 206 00:13:09,360 --> 00:13:12,000 This transition from gigantic to miniature, 207 00:13:12,160 --> 00:13:14,000 between exterior and interior, 208 00:13:14,160 --> 00:13:16,960 shows that the Nabataeans knew about force dynamics, 209 00:13:17,120 --> 00:13:19,880 and were careful to evaluate the risk of collapse. 210 00:13:20,040 --> 00:13:23,840 You need to triangulate any loading, 211 00:13:24,000 --> 00:13:28,640 so that it can go over the structure and back down to the earth, 212 00:13:28,800 --> 00:13:33,320 and if you hollow it out to too great an extent, it would collapse 213 00:13:33,480 --> 00:13:36,360 and it would have brought the facade down with it. 214 00:13:47,840 --> 00:13:52,360 These modest rooms pose question about the very nature of Al-Khazneh. 215 00:13:53,440 --> 00:13:57,640 Even today, experts still can't agree on its exact function. 216 00:14:08,800 --> 00:14:12,480 One thing is for sure, this structure was designed to impress. 217 00:14:12,640 --> 00:14:15,680 It is the first thing you see when entering the site. 218 00:14:15,840 --> 00:14:19,280 Thanks to the support of the cliff, the Nabataeans ensured 219 00:14:19,440 --> 00:14:24,440 that this spectacular monument would remain standing 2000 years later. 220 00:14:26,000 --> 00:14:29,160 For centuries, Petra has survived many dangers - 221 00:14:29,320 --> 00:14:32,440 erosion, earthquakes, enemy attacks. 222 00:14:32,600 --> 00:14:35,520 But the city also has to withstand another major challenge. 223 00:14:35,680 --> 00:14:38,480 A hazard that's unexpected in the desert. 224 00:14:39,680 --> 00:14:42,840 From this blue sky, it's hard to believe 225 00:14:43,000 --> 00:14:45,560 how it mists up during the winter season. 226 00:14:45,720 --> 00:14:48,000 THUNDER RUMBLES 227 00:14:48,160 --> 00:14:53,080 Between October and January, the city can be hit by torrential rain. 228 00:14:53,240 --> 00:14:56,160 And the rain here always starts suddenly. 229 00:14:56,320 --> 00:15:01,400 The other side of this is that there is the danger of flash floods. 230 00:15:01,560 --> 00:15:03,560 In the event of a storm, 231 00:15:03,720 --> 00:15:08,040 rainwater flows between gaps in the rock and funnels toward the Siq. 232 00:15:08,200 --> 00:15:11,480 This natural gorge can transform into a furious torrent 233 00:15:11,640 --> 00:15:15,120 threatening the entire city, starting with Al-Khazneh. 234 00:15:16,280 --> 00:15:19,760 Even in my 12 years here, there were two times where you saw 235 00:15:19,920 --> 00:15:23,480 the water roll into centre city and wreak havoc, 236 00:15:23,640 --> 00:15:26,080 that major boulders moved along. 237 00:15:26,240 --> 00:15:29,600 And you realised that people needed to be evacuated out of the city. 238 00:15:29,760 --> 00:15:35,120 In November 2018, 4000 tourists had to be urgently evacuated 239 00:15:35,280 --> 00:15:38,520 to avoid being trapped by devastating mudslides. 240 00:15:39,840 --> 00:15:43,800 But what did the Nabataens do when faced with this danger? 241 00:15:43,960 --> 00:15:45,280 To answer this question, 242 00:15:45,440 --> 00:15:47,840 archaeologists first looked for clues at the Siq - 243 00:15:48,000 --> 00:15:50,440 the narrow gorge that allows access to the city. 244 00:15:50,600 --> 00:15:53,000 The Siq was the weakest point 245 00:15:53,160 --> 00:15:57,560 of entire infrastructure of the city of Petra, 246 00:15:57,720 --> 00:16:02,480 so they had to protect this paved road from destruction. 247 00:16:04,080 --> 00:16:06,880 During the first excavations in the 19th century, 248 00:16:07,040 --> 00:16:11,520 archaeologists discovered an amazing passage carved through the rock. 249 00:16:12,720 --> 00:16:17,240 A tunnel, three metres wide and five metres high, leading to a canal. 250 00:16:19,080 --> 00:16:20,680 We're now in the middle of 251 00:16:20,840 --> 00:16:24,440 one of the most impressive hydrological structures in Petra. 252 00:16:24,600 --> 00:16:27,920 This tunnel was partly cut in the rock 2000 years ago. 253 00:16:28,080 --> 00:16:31,720 This tunnel was associated with another diversion dam 254 00:16:31,880 --> 00:16:34,480 that was constructed not far away from it 255 00:16:34,640 --> 00:16:36,960 and both structures were constructed 256 00:16:37,120 --> 00:16:39,400 in order to manage the water floods 257 00:16:39,560 --> 00:16:42,160 and prevent them from entering the city. 258 00:16:44,160 --> 00:16:46,560 The dam was built near the city's entrance, 259 00:16:46,720 --> 00:16:50,320 diverting water towards the tunnel and away from the Siq. 260 00:16:50,480 --> 00:16:54,880 An ingenious solution that prevented the destruction of Petra's jewel. 261 00:17:01,520 --> 00:17:05,320 Other dams, discovered later, completed this protection system. 262 00:17:07,360 --> 00:17:10,400 Ahmad Hasanat is an expert in digital archaeology. 263 00:17:10,560 --> 00:17:14,760 By taking thousands of pictures of the protection system's remains, 264 00:17:14,920 --> 00:17:19,840 he has been able to make 3D digital models of 36 individual sites. 265 00:17:20,000 --> 00:17:22,480 We are standing in one of these dams 266 00:17:22,640 --> 00:17:27,640 which is a clear example about how the Nabateans 267 00:17:27,800 --> 00:17:31,120 used to protect their cities from flash floods. 268 00:17:31,280 --> 00:17:35,880 Today, most of the dams have been restored and returned to service. 269 00:17:39,200 --> 00:17:42,320 Nabataean system was re-erected 270 00:17:42,480 --> 00:17:45,480 by the Jordanian department of Antiquities 271 00:17:45,640 --> 00:17:50,880 for the protection of people, tourists going into Petra. 272 00:17:51,640 --> 00:17:55,400 It's the first time ever in history of archaeology 273 00:17:55,560 --> 00:17:59,680 that I did archaeology not only for curiosity 274 00:17:59,840 --> 00:18:03,200 but to get to know how the system works 275 00:18:03,360 --> 00:18:06,120 and whether it's possible to restore it, 276 00:18:06,280 --> 00:18:09,600 that it works again, and that's what I did, it works again. 277 00:18:10,640 --> 00:18:15,200 The system still functions and is proving to be an ingenious feature. 278 00:18:18,280 --> 00:18:21,480 Because the Nabataeans faced another major problem - 279 00:18:21,640 --> 00:18:24,520 how to supply the city with water all year round 280 00:18:24,680 --> 00:18:26,840 when it only rains in winter? 281 00:18:30,760 --> 00:18:34,640 It has 200 millimetres of water a year, 282 00:18:34,800 --> 00:18:37,800 whereas in Western Europe we have 900. 283 00:18:37,960 --> 00:18:39,680 They needed to harness that. 284 00:18:39,840 --> 00:18:41,760 There is no life without water. 285 00:18:42,680 --> 00:18:46,640 How did the city's 30,000 inhabitants obtain fresh water? 286 00:18:47,800 --> 00:18:50,840 And how did they cultivate the land to feed themselves? 287 00:18:51,000 --> 00:18:56,400 The water at Petra has a reliable source up in the mountains. 288 00:18:58,040 --> 00:19:00,320 But it is some distance from the city. 289 00:19:03,160 --> 00:19:07,440 Satellite imagery reveals that the closest waterway, the Ain Moussa, 290 00:19:07,600 --> 00:19:09,880 is situated 9km away. 291 00:19:10,400 --> 00:19:13,840 So how did ancient engineers provide drinking water 292 00:19:14,000 --> 00:19:20,000 to the city's inhabitants, without a nearby water source or regular rain? 293 00:19:20,800 --> 00:19:23,320 The first answer can be found at the dams - 294 00:19:23,480 --> 00:19:26,160 built to protect the city from flash floods. 295 00:19:26,840 --> 00:19:28,880 So Nabataeans built this, 296 00:19:29,040 --> 00:19:33,320 first of all to protect the city from the flash floods, 297 00:19:33,480 --> 00:19:35,520 and then to use the water, to collect the water, 298 00:19:35,680 --> 00:19:37,960 because they were very careful and wise 299 00:19:38,120 --> 00:19:39,680 to collect every drop of water. 300 00:19:39,840 --> 00:19:43,080 Every drop of rain that trickled down the rock face 301 00:19:43,240 --> 00:19:47,440 was channelled and directed into water tanks where it could be stored. 302 00:19:48,680 --> 00:19:51,400 There were as many as 200 tanks in the city. 303 00:19:51,560 --> 00:19:53,920 Many are still visible to the naked eye. 304 00:19:54,080 --> 00:19:57,960 Some from high up, others like this one, from the ground. 305 00:19:59,360 --> 00:20:01,000 But there was a problem. 306 00:20:01,160 --> 00:20:04,640 The water that collected in these tanks wasn't drinkable. 307 00:20:05,960 --> 00:20:09,440 It was not only water, it was dung from the birds, 308 00:20:09,600 --> 00:20:14,960 it was branches from bushes, it was dry leaves, god knows what. 309 00:20:15,120 --> 00:20:19,400 And then the water had to be collected and to still down, 310 00:20:19,560 --> 00:20:26,200 and then all the material fell down to the bottom. 311 00:20:27,400 --> 00:20:32,040 In 1999, Ueli Bellwald carried out tests on the rainwater. 312 00:20:32,200 --> 00:20:34,240 The results allowed him to understand 313 00:20:34,400 --> 00:20:36,440 how the Nabataeans obtained drinking water. 314 00:20:36,600 --> 00:20:39,040 They stored water in a first pool 315 00:20:39,200 --> 00:20:41,640 and waited for the waste to sink to the bottom 316 00:20:41,800 --> 00:20:43,800 then the water flowed into a second pool 317 00:20:43,960 --> 00:20:47,880 followed by a third, controlled by a system of valves. 318 00:20:48,520 --> 00:20:51,360 From the first to the next to the next, 319 00:20:51,520 --> 00:20:57,160 and at the end of this filtering process, the water was really clean. 320 00:20:58,120 --> 00:21:02,040 This filtration system made the water cleaner for drinking. 321 00:21:03,360 --> 00:21:05,880 But how did it reach the city? 322 00:21:07,160 --> 00:21:10,240 The answer can be found here in the Siq. 323 00:21:10,400 --> 00:21:14,240 On either side of this narrow rocky gorge are shallow grooves 324 00:21:14,400 --> 00:21:17,680 that Ahmad Hasanat thinks were carved by the Nabataeans. 325 00:21:20,800 --> 00:21:22,760 One diverted rainwater. 326 00:21:23,960 --> 00:21:27,760 The other channelled in spring water from the neighbouring mountains. 327 00:21:32,760 --> 00:21:36,160 Actually there is a complicated system of pipelines 328 00:21:36,320 --> 00:21:38,880 to provide the water for every single house. 329 00:21:40,480 --> 00:21:44,960 So every single house in Petra gets the water like our days. 330 00:21:46,120 --> 00:21:49,160 Thanks to his meticulous digital work, 331 00:21:49,320 --> 00:21:51,520 Ahmad was able to compile details 332 00:21:51,680 --> 00:21:55,320 of all of the discoveries made by previous archaeologists. 333 00:21:55,480 --> 00:21:57,520 It allowed him to build a complete map 334 00:21:57,680 --> 00:22:00,480 of the complex Nabataeans' hydraulic system. 335 00:22:00,640 --> 00:22:03,840 29km of pipes and five aqueducts 336 00:22:04,000 --> 00:22:07,680 that channelled an astonishing 46 million litres of water 337 00:22:07,840 --> 00:22:10,080 into the city each day. 338 00:22:14,400 --> 00:22:16,920 A change of scale allows us to discover 339 00:22:17,080 --> 00:22:20,200 other elements of this stunning hydraulic system. 340 00:22:21,200 --> 00:22:22,840 Some of the rock-cut channels 341 00:22:23,000 --> 00:22:25,760 retain the faint traces of terracotta pipes. 342 00:22:26,640 --> 00:22:28,120 If we look up close here, 343 00:22:28,280 --> 00:22:31,160 we can see that the edge of these pottery pipes, 344 00:22:31,320 --> 00:22:34,760 and also we can see how these pipes connected together. 345 00:22:35,840 --> 00:22:38,800 The Nabataeans developed a system of pipes 346 00:22:38,960 --> 00:22:40,960 that was highly advanced for the time. 347 00:22:42,880 --> 00:22:45,400 Terracotta pipes were embedded into the rock, 348 00:22:45,560 --> 00:22:47,160 fixed in place with mortar 349 00:22:47,320 --> 00:22:50,000 and the joints sealed with a waterproof coating. 350 00:22:51,840 --> 00:22:55,920 They made first a clay like the paste for bread 351 00:22:56,080 --> 00:23:01,920 and then they wrapped this clay paste around a wooden cylinder 352 00:23:02,080 --> 00:23:04,520 and fixed the two ends together 353 00:23:04,680 --> 00:23:08,480 and then they were firing these enormous pieces. 354 00:23:10,040 --> 00:23:14,360 These terracotta pipelines preserved the quality of drinking water. 355 00:23:16,400 --> 00:23:19,360 But the Nabataeans faced another major problem. 356 00:23:19,520 --> 00:23:23,120 How could these pipes withstand enormous pressure 357 00:23:23,280 --> 00:23:25,960 created by the steep slope between the source, 358 00:23:26,120 --> 00:23:28,520 at an altitude of 1300 metres, 359 00:23:28,680 --> 00:23:32,760 and the centre of the city 500 metres below? 360 00:23:33,840 --> 00:23:38,080 Inside the pipelines, with each percent of gradient, 361 00:23:38,240 --> 00:23:43,840 the pressure inside the pipeline increases by one bar. 362 00:23:44,000 --> 00:23:48,840 We know from tests that these terracotta pipes could bear 363 00:23:49,000 --> 00:23:52,280 an internal pressure of 9 bars. 364 00:23:53,320 --> 00:23:57,800 With a slope between 4 and 5 percent, terracotta pipes won't explode 365 00:23:57,960 --> 00:24:00,240 but they still remain 80% filled with water, 366 00:24:00,400 --> 00:24:02,640 allowing for a regular flow. 367 00:24:02,800 --> 00:24:05,960 This is exactly the angle of the channels discovered in Petra. 368 00:24:06,640 --> 00:24:09,680 Through experience, the Nabataeans had managed to determine 369 00:24:09,840 --> 00:24:12,840 the perfect angle for their pipeline to withstand the pressure - 370 00:24:13,000 --> 00:24:14,600 another feat for the era - 371 00:24:14,760 --> 00:24:16,840 while their system of aqueducts and valves 372 00:24:17,000 --> 00:24:20,120 let them adjust the flow rate in their hydraulic network. 373 00:24:20,280 --> 00:24:25,000 Now, the city could be supplied with sufficient water all year round. 374 00:24:25,160 --> 00:24:26,440 In Petra, 375 00:24:26,600 --> 00:24:30,400 the population which grew to 30,000 people, 376 00:24:30,560 --> 00:24:32,960 could rely on being able to drink 377 00:24:33,120 --> 00:24:35,120 eight litres of water a day. 378 00:24:35,280 --> 00:24:40,800 They could rely on about 40,000 cubic metres of water per day, 379 00:24:40,960 --> 00:24:43,480 which makes it really incredible. 380 00:24:43,640 --> 00:24:48,440 It means that they had water not only for the normal domestic uses 381 00:24:48,600 --> 00:24:50,680 but also for public uses. 382 00:24:50,840 --> 00:24:53,480 The Nabataeans figured out how to transport 383 00:24:53,640 --> 00:24:56,400 an incredible volume of water into the middle of the desert. 384 00:24:56,560 --> 00:24:58,440 But what could they use this abundance for? 385 00:24:58,600 --> 00:25:00,680 In the heart of the city, 386 00:25:00,840 --> 00:25:04,160 the study of ruins next to the Great Temple reveals something astonishing. 387 00:25:04,440 --> 00:25:06,600 At first glance, these piled slabs and pebbles 388 00:25:06,760 --> 00:25:08,800 don't suggest the presence of water. 389 00:25:08,960 --> 00:25:11,840 The first archaeologists even thought this was a marketplace. 390 00:25:12,120 --> 00:25:16,280 But, in 2013, a study of soils on a microscopic scale 391 00:25:16,440 --> 00:25:19,280 made it possible to make an incredible discovery. 392 00:25:19,800 --> 00:25:24,400 And through the archaeologist analysis for sand samples, 393 00:25:24,560 --> 00:25:29,520 they have proved that those samples have seeds of palm tree. 394 00:25:29,680 --> 00:25:32,080 Which give us the idea that 395 00:25:32,240 --> 00:25:38,560 this garden was full of palm tree as the main tree for the garden. 396 00:25:38,720 --> 00:25:40,880 Amongst the grains of sand, 397 00:25:41,040 --> 00:25:44,600 scientists found remains of fossilised seeds and plants. 398 00:25:44,760 --> 00:25:47,520 Which meant that the Nabataeans had mastered irrigation 399 00:25:47,680 --> 00:25:49,520 to create lush gardens. 400 00:25:49,680 --> 00:25:51,080 And that's not all. 401 00:25:51,880 --> 00:25:54,360 By analysing the ground with georadar, 402 00:25:54,520 --> 00:25:57,720 researchers have detected the presence of an enormous pool. 403 00:25:57,880 --> 00:25:59,360 Instead of a market, 404 00:25:59,520 --> 00:26:02,200 there used to be an incredible aquatic complex here 405 00:26:02,360 --> 00:26:06,240 which today's digital imagery makes it possible to recreate. 406 00:26:10,760 --> 00:26:16,080 Above the garden, there is this unique swimming pool. 407 00:26:16,240 --> 00:26:18,840 And this swimming pool 408 00:26:19,000 --> 00:26:25,080 is about 44 by 25 metres and about 2 metres of depth. 409 00:26:25,240 --> 00:26:29,600 It's actually like the size of Olympic swimming pool nowadays. 410 00:26:31,320 --> 00:26:35,080 An Olympic-sized swimming pool, one century before Christ. 411 00:26:35,240 --> 00:26:38,400 It seems excessive in a desert where water is so precious. 412 00:26:39,160 --> 00:26:41,760 But the abundance of water was key to the Nabataeans 413 00:26:41,920 --> 00:26:44,560 establishing their power in the region. 414 00:26:45,200 --> 00:26:48,280 Water was used to serve the city's splendour. 415 00:27:00,040 --> 00:27:01,920 The mastery of the water 416 00:27:02,080 --> 00:27:05,920 and then creating these cascading fountains and pools, 417 00:27:06,080 --> 00:27:08,000 it's basically showing off. 418 00:27:10,200 --> 00:27:13,440 The Nabataeans were originally nomads, caravan drivers. 419 00:27:13,600 --> 00:27:15,120 They knew that in the desert, 420 00:27:15,280 --> 00:27:17,720 water is the most important source of wealth. 421 00:27:18,400 --> 00:27:20,480 And they took full advantage of it. 422 00:27:23,120 --> 00:27:26,120 In terms of Nabatean economy, it relied heavily on trade. 423 00:27:26,280 --> 00:27:30,440 The main trade that brought the most money 424 00:27:30,600 --> 00:27:32,960 was the trade of incense and myrrh. 425 00:27:33,120 --> 00:27:34,480 In ancient times, 426 00:27:34,640 --> 00:27:37,880 incense and myrrh were luxurious, rare and expensive goods. 427 00:27:38,040 --> 00:27:43,120 Petra became so rich due do its location at a strategic crossroads. 428 00:28:08,600 --> 00:28:11,720 Today, archaeologists and historians believe 429 00:28:11,880 --> 00:28:14,320 that the abundance of water and luxury in the city 430 00:28:14,480 --> 00:28:17,400 were key to the success of the Nabataean people. 431 00:28:18,280 --> 00:28:21,560 Petra demonstrates opulence 432 00:28:21,720 --> 00:28:25,680 and people would be drawn from great distances 433 00:28:25,840 --> 00:28:28,680 to come and marvel at this society 434 00:28:28,840 --> 00:28:31,960 and also to spend money there. 435 00:28:32,120 --> 00:28:36,840 It was a financial Mecca, a Las Vegas of its time. 436 00:28:38,480 --> 00:28:41,120 The city stood out as a place of opulence. 437 00:28:41,280 --> 00:28:44,280 It was the Dubai or Las Vegas of its time. 438 00:28:44,440 --> 00:28:47,520 In Petra, everything was made to dazzle visitors. 439 00:28:47,680 --> 00:28:50,560 Al-Khazneh, as well as other monuments. 440 00:29:17,640 --> 00:29:19,200 Today scientists are studying 441 00:29:19,360 --> 00:29:22,440 the remains of 850 buildings from every angle. 442 00:29:22,600 --> 00:29:26,520 They want to understand how the city developed over the centuries. 443 00:29:26,680 --> 00:29:29,720 These constructions have suffered the ravages of time 444 00:29:29,880 --> 00:29:32,280 much more than those which were carved into the cliffs. 445 00:29:32,440 --> 00:29:34,960 However, thanks to new technology, 446 00:29:35,120 --> 00:29:37,600 experts can reveal their full splendour. 447 00:29:37,760 --> 00:29:40,880 In the heights of the city, at the summit of Jabal Khubtat, 448 00:29:41,040 --> 00:29:44,200 a French archaeological mission has taken an interest in these ruins, 449 00:29:44,360 --> 00:29:47,480 which were first discovered at the start of last century. 450 00:29:47,640 --> 00:29:49,560 So this is the place? Yes, that's the place, 451 00:29:49,720 --> 00:29:51,000 I think we should stand here. 452 00:29:51,160 --> 00:29:54,800 Archaeologists have long believed that this was a place of worship. 453 00:29:54,960 --> 00:29:56,560 To verify this theory, 454 00:29:56,720 --> 00:30:00,000 Thibaud Fournet is focussed on recreating the entire building. 455 00:30:00,160 --> 00:30:03,200 He will use drone photography to achieve his goal. 456 00:30:03,360 --> 00:30:06,840 I need the main pictures on this main monument 457 00:30:07,000 --> 00:30:08,760 from this angle to this one, 458 00:30:08,920 --> 00:30:12,400 on different flights, from the top and the front of the cliff. 459 00:30:20,280 --> 00:30:23,080 By employing a drone to photograph these remains 460 00:30:23,240 --> 00:30:24,800 from many different angles, 461 00:30:24,960 --> 00:30:27,160 photogrammetry can be used to visualise 462 00:30:27,320 --> 00:30:30,040 the dimensions and volumes of the ruined buildings 463 00:30:30,200 --> 00:30:31,920 and reveal their architecture. 464 00:30:59,760 --> 00:31:03,040 3-dimensional re-creations, in conjunction with excavation work 465 00:31:03,200 --> 00:31:05,240 has revealed a building measuring 225 square metres, 466 00:31:06,240 --> 00:31:07,680 and composed of seven rooms. 467 00:31:07,840 --> 00:31:10,080 And the research shows something surprising. 468 00:31:10,240 --> 00:31:12,120 This wasn't a place of worship 469 00:31:12,280 --> 00:31:14,680 but an incredible spa hanging from the cliff. 470 00:31:30,720 --> 00:31:32,440 Thanks to these digital models, 471 00:31:32,600 --> 00:31:35,680 Thibaud could even reconstruct the exact path taken by bathers 472 00:31:35,840 --> 00:31:37,760 who visited this luxurious spa. 473 00:32:06,320 --> 00:32:10,080 According to Thibault, this layout is typical of the thermal architecture 474 00:32:10,240 --> 00:32:11,920 from Latin civilisation. 475 00:32:12,080 --> 00:32:15,600 The Nabataeans must have built these baths under Roman influence. 476 00:32:16,600 --> 00:32:18,640 Historians believe that these invaders 477 00:32:18,800 --> 00:32:21,000 took over Petra without a fight. 478 00:32:21,160 --> 00:32:24,440 It became a Roman province in 106 A.D. 479 00:32:25,840 --> 00:32:29,440 Today, scientists are trying to understand how the Romans influenced, 480 00:32:29,600 --> 00:32:31,800 or even changed the city's architecture. 481 00:32:48,600 --> 00:32:53,000 When flying over the site, traces of Roman presence are evident. 482 00:32:53,160 --> 00:32:55,600 Like this impressive ancient amphitheatre - 483 00:32:55,760 --> 00:32:57,440 33 rows of seats, 484 00:32:57,600 --> 00:33:02,640 and a 50-metre orchestra area holding 5000 spectators. 485 00:33:02,800 --> 00:33:04,720 But other sites can only be uncovered 486 00:33:04,880 --> 00:33:07,680 through the development of complex investigative techniques. 487 00:33:07,840 --> 00:33:10,120 Shall we go up and set up there? Yes. 488 00:33:10,280 --> 00:33:13,040 For several years, French experts have been investigating 489 00:33:13,200 --> 00:33:17,400 one of Petra's most important monuments - the Qasr al-Bint temple 490 00:33:17,560 --> 00:33:20,560 literally meaning "the castle of the pharaoh's daughter". 491 00:33:20,720 --> 00:33:24,480 This building was constructed by the Nabataeans around 30 A.D. 492 00:33:35,120 --> 00:33:38,360 The monument has been severely damaged over time. 493 00:33:52,320 --> 00:33:55,160 Francois Renel leads a team of ten archaeologists 494 00:33:55,320 --> 00:33:57,520 supported by ten Jordanian workers. 495 00:33:57,680 --> 00:34:00,640 They are meticulously excavating the ruins of the temple. 496 00:34:06,760 --> 00:34:10,040 The team is hunting for traces of the Roman building works. 497 00:34:38,440 --> 00:34:40,440 The Romans added their own materials 498 00:34:40,600 --> 00:34:43,960 to the top of the limestone and sandstone of the Nabataean buildings. 499 00:34:44,240 --> 00:34:47,600 Materials like white marble which they considered more precious. 500 00:34:48,880 --> 00:34:51,960 Experts believe they changed this Nabataean place of worship 501 00:34:52,120 --> 00:34:55,280 into a temple dedicated to the glory of their Gods. 502 00:35:16,040 --> 00:35:19,560 The team have carried out a detailed topographical survey of the site 503 00:35:19,720 --> 00:35:22,600 allowing them to recreate the dimensions and volume 504 00:35:22,760 --> 00:35:24,280 of the Qasr al-Bint. 505 00:35:24,440 --> 00:35:27,640 Then modelling software could bring these ruins back to life, 506 00:35:27,800 --> 00:35:29,720 recreating, in three dimensions, 507 00:35:29,880 --> 00:35:32,480 the structure as it looked 2000 years ago. 508 00:35:35,160 --> 00:35:39,720 Thanks to the Roman Empire, Petra experienced glory days once again. 509 00:35:39,880 --> 00:35:42,920 But without the architectural genius of the Nabataeans, 510 00:35:43,080 --> 00:35:45,920 these constructions would have disappeared long ago, 511 00:35:46,080 --> 00:35:47,640 wiped out by earthquakes. 512 00:35:47,800 --> 00:35:51,280 To understand how, it's necessary to take to the sky. 513 00:35:51,440 --> 00:35:53,160 Satellite imagery reveals 514 00:35:53,320 --> 00:35:56,520 the very particular geographical situation of this site. 515 00:35:56,680 --> 00:35:58,680 Petra was built over a seismic fault. 516 00:35:58,840 --> 00:36:01,560 The city is on the boundary of two sliding plates - 517 00:36:01,720 --> 00:36:04,080 the African plate and the Arabian plate. 518 00:36:05,080 --> 00:36:09,240 In this area, two continental plates are moving. 519 00:36:09,400 --> 00:36:12,600 One is shifting below the other 520 00:36:12,760 --> 00:36:14,920 and the other one is shifting over. 521 00:36:15,080 --> 00:36:17,160 As the plates slide over each other, 522 00:36:17,320 --> 00:36:20,400 they can cause particularly violent earthquakes. 523 00:36:20,560 --> 00:36:22,720 We think about Petra and we should always remember 524 00:36:22,880 --> 00:36:26,760 that there were many earthquakes that influenced the city's history. 525 00:36:26,920 --> 00:36:32,240 The biggest one was in May 363 and devastated the centre city of Petra. 526 00:36:47,480 --> 00:36:49,720 Archaeologists have studied the Qasr al-Bint 527 00:36:49,880 --> 00:36:52,880 in an attempt to understand how it could survive centuries 528 00:36:53,040 --> 00:36:54,880 in this highly seismic zone. 529 00:36:55,040 --> 00:36:57,080 Within the partially destroyed walls, 530 00:36:57,240 --> 00:37:00,240 they found a clue - the remains of wood. 531 00:37:00,400 --> 00:37:04,200 Some experts think that this is the key to withstanding tremors. 532 00:37:04,360 --> 00:37:06,640 Their engineers, they understood 533 00:37:06,800 --> 00:37:09,160 that they needed to deal with the tectonic problems. 534 00:37:10,240 --> 00:37:12,640 The Nabataean engineers had invented 535 00:37:12,800 --> 00:37:16,240 one of the first anti-seismic measures in history. 536 00:37:16,720 --> 00:37:18,360 They had this idea 537 00:37:18,520 --> 00:37:21,440 that this piece of wood in the middle of the building 538 00:37:21,600 --> 00:37:24,200 should control the cracks, 539 00:37:24,360 --> 00:37:28,240 the vertical and the horizontal cracks within the building. 540 00:37:31,560 --> 00:37:33,920 Experts think that the framework of wooden beams, 541 00:37:34,080 --> 00:37:37,080 made of a more flexible material than the stone around it 542 00:37:37,240 --> 00:37:39,080 absorbs the energy of earthquakes 543 00:37:39,240 --> 00:37:41,880 combatting the effects of stress in the walls, 544 00:37:42,040 --> 00:37:46,080 the raising of foundations and even twisting. 545 00:37:46,240 --> 00:37:49,760 Somehow, it's controlling the balance of the building 546 00:37:49,920 --> 00:37:55,040 which makes a smooth movement in the blocks of the building 547 00:37:55,200 --> 00:37:57,920 and this technique is actually approved, 548 00:37:58,080 --> 00:37:59,680 this is a successful technique. 549 00:37:59,840 --> 00:38:03,760 The Nabataeans had risen to the challenge posed by earthquakes 550 00:38:03,920 --> 00:38:06,440 and they even took some benefit from the phenomenon. 551 00:38:06,600 --> 00:38:08,640 Because it was seismic activity 552 00:38:08,800 --> 00:38:11,480 that created this city's exceptional scenery. 553 00:38:11,640 --> 00:38:13,600 In Greek, Petra means "stone" 554 00:38:13,760 --> 00:38:16,280 and it is this extraordinary raw material 555 00:38:16,440 --> 00:38:18,520 that gave its name to the city. 556 00:38:19,080 --> 00:38:20,880 But what is so particular about it? 557 00:38:21,040 --> 00:38:23,800 And how did the Nabataeans manage to work with it? 558 00:38:23,960 --> 00:38:26,120 It's not possible to understand Petra 559 00:38:26,280 --> 00:38:29,160 without understanding its geology. 560 00:38:36,240 --> 00:38:38,560 Petra is carved in a natural rock 561 00:38:38,720 --> 00:38:43,720 so it is important to understand the raw material. 562 00:38:44,200 --> 00:38:46,800 Seismic activity allowed the raw building materials 563 00:38:46,960 --> 00:38:49,720 used by the Nabataeans to rise to the surface. 564 00:38:49,880 --> 00:38:52,360 This is a sedimentary rock called sandstone 565 00:38:52,520 --> 00:38:54,360 with very specific properties. 566 00:38:54,600 --> 00:38:59,760 Petra is surrounded by mountains that are made of igneous rocks. 567 00:38:59,920 --> 00:39:02,440 But Petra itself is sandstone 568 00:39:02,600 --> 00:39:07,280 and sandstone is formed by layers effectively under the sea. 569 00:39:07,440 --> 00:39:11,800 And that means this sandstone is not like granite, 570 00:39:11,960 --> 00:39:18,040 a stone which is strong and compact, 571 00:39:18,200 --> 00:39:20,080 but it's only like cement, 572 00:39:20,240 --> 00:39:23,400 the grains are still the same as they ever were 573 00:39:23,560 --> 00:39:25,800 but they are glued together by lime. 574 00:39:25,960 --> 00:39:28,800 When you observe sandstone under a microscope, 575 00:39:28,960 --> 00:39:30,840 you realise that it is composed of 576 00:39:31,000 --> 00:39:33,440 millions of compressed grains of sand. 577 00:39:33,600 --> 00:39:37,640 This characteristic explains how the stone is so easily cut. 578 00:39:37,880 --> 00:39:40,400 To work it, the Nabataeans could resort 579 00:39:40,560 --> 00:39:42,080 to relatively basic techniques. 580 00:39:42,240 --> 00:39:47,200 Some of their tools even left marks that are studied by scientists today. 581 00:40:05,440 --> 00:40:06,880 It shows one way 582 00:40:07,040 --> 00:40:09,400 the Nabataeans enhanced the beauty of their landscape. 583 00:40:09,560 --> 00:40:11,280 When flying over Petra, 584 00:40:11,440 --> 00:40:14,720 the variety of colour in the monuments is impressive. 585 00:40:14,880 --> 00:40:21,320 The colours and the design in the bedrock itself, 586 00:40:21,480 --> 00:40:23,280 it's very, very impressive. 587 00:40:23,440 --> 00:40:26,600 An extraordinary range which stretches from yellow to purple, 588 00:40:26,760 --> 00:40:29,080 as well as pinks, oranges and reds. 589 00:40:29,240 --> 00:40:31,320 This is the only place 590 00:40:31,480 --> 00:40:34,200 where sandstone becomes art. 591 00:40:34,360 --> 00:40:37,160 The colours of Petra are just amazing. 592 00:40:37,320 --> 00:40:41,680 You cannot stop looking or gazing at the facades of Petra. 593 00:40:43,640 --> 00:40:46,600 The builders understood that to embellish the city, 594 00:40:46,760 --> 00:40:49,240 they could utilise the incredible range of colours 595 00:40:49,400 --> 00:40:51,600 that the sandstone naturally offered. 596 00:40:53,120 --> 00:40:56,600 All different colours of sandstone of Petra are visible. 597 00:40:56,760 --> 00:41:01,000 Each single layer represents the different chemical compositions 598 00:41:01,160 --> 00:41:08,200 depending on the typology of iron oxide which is present inside. 599 00:41:08,360 --> 00:41:12,560 When sandstone forms, it preserves a record of the different types of sand 600 00:41:12,880 --> 00:41:14,520 deposited over time. 601 00:41:14,680 --> 00:41:17,520 And one element is particularly spectacular. 602 00:41:18,800 --> 00:41:22,960 There's so much embedded quartzite in the sandstone, 603 00:41:23,120 --> 00:41:25,160 it refracts the light 604 00:41:25,320 --> 00:41:29,600 and so you get these different coloured grains within the sand, 605 00:41:29,760 --> 00:41:31,920 which through this reflection, 606 00:41:32,080 --> 00:41:35,560 makes all these different colours and different bands, 607 00:41:35,720 --> 00:41:38,000 which brings the sculpture to life. 608 00:41:38,160 --> 00:41:42,000 It would be dead without that geological composition. 609 00:41:43,440 --> 00:41:46,800 It's the composition of the sandstone, in part thanks to quartz, 610 00:41:46,960 --> 00:41:48,800 that gives the city its splendour. 611 00:41:48,960 --> 00:41:52,040 The Nabataeans used the colours of this rock to great effect, 612 00:41:52,200 --> 00:41:55,200 but they also suffered from this stone's weaknesses. 613 00:41:58,840 --> 00:42:02,280 Because the strength of sandstone varies greatly. 614 00:42:02,440 --> 00:42:04,720 By choosing to carve their structures here, 615 00:42:04,880 --> 00:42:07,640 the builders were taking a big risk. 616 00:42:19,000 --> 00:42:21,320 It's likely that the instability of the rock 617 00:42:21,480 --> 00:42:23,800 accounts for the number of construction sites 618 00:42:23,960 --> 00:42:25,440 found abandoned here. 619 00:42:42,480 --> 00:42:45,960 Even today, the nature of the stone poses a threat to Petra. 620 00:42:46,120 --> 00:42:48,800 A team of scientists from UNESCO, 621 00:42:48,960 --> 00:42:51,800 led by Georgia Cesario and Giuseppe Delmonaco, 622 00:42:51,960 --> 00:42:54,440 have the delicate task of securing this site 623 00:42:54,600 --> 00:42:57,160 and safeguarding this jewel of the desert. 624 00:42:57,760 --> 00:43:00,560 All the monuments are affected by similar factors 625 00:43:00,720 --> 00:43:02,200 like wind and water erosion. 626 00:43:03,840 --> 00:43:06,800 It's really fundamental for the people who take care of the site 627 00:43:06,960 --> 00:43:12,640 to understand this concept in order to act and to prioritise. 628 00:43:13,880 --> 00:43:15,840 The most fragile area is the Siq - 629 00:43:16,000 --> 00:43:20,000 the passage through which half a million tourists pass each year. 630 00:43:24,040 --> 00:43:26,720 In May 2019, just in the place where I am, 631 00:43:26,880 --> 00:43:31,320 a small stone fell from the top of this cliff, 632 00:43:31,480 --> 00:43:35,160 which is one of the highest points in the site itself. 633 00:43:35,320 --> 00:43:37,840 And fortunately it happened in the night 634 00:43:38,000 --> 00:43:41,480 and so we didn't have any injuries for the visitors. 635 00:43:41,640 --> 00:43:46,920 But in May 2015, a big block fell from this cliff. 636 00:43:47,080 --> 00:43:51,880 It happened around 11 o'clock when people were passing through. 637 00:43:52,800 --> 00:43:55,800 Today, new technology like GPS sensors 638 00:43:55,960 --> 00:43:58,560 give advance warnings of this type of accident. 639 00:44:00,480 --> 00:44:03,880 Eleven dangerous spots have been identified at the Siq 640 00:44:04,040 --> 00:44:06,800 and Georgia's team, aided by rock climbing specialists, 641 00:44:06,960 --> 00:44:08,560 have installed nets in the areas 642 00:44:08,720 --> 00:44:11,440 where the rock is most likely to crumble. 643 00:44:13,520 --> 00:44:18,080 Then the team installed a highly sophisticated surveillance system. 644 00:44:19,320 --> 00:44:21,280 On the top of the block, 645 00:44:21,440 --> 00:44:26,120 we put a thermometer and a tiltmeter to measure the inclination in time. 646 00:44:27,120 --> 00:44:30,360 This device monitors the rock 24 hours a day 647 00:44:30,520 --> 00:44:32,280 sending alerts to the UNESCO team 648 00:44:32,440 --> 00:44:36,520 who can intervene in the event of danger and evacuate the Siq. 649 00:44:39,360 --> 00:44:41,960 Through fieldwork and thanks to digital models, 650 00:44:42,120 --> 00:44:43,960 scientists today are trying to bring 651 00:44:44,120 --> 00:44:46,600 the ancient city of Petra back to life. 652 00:44:46,760 --> 00:44:48,440 For centuries the city was abandoned, 653 00:44:48,600 --> 00:44:51,280 and even the Nabataeans' architectural genius 654 00:44:51,440 --> 00:44:54,360 wasn't enough to ensure they would be remembered. 655 00:44:54,520 --> 00:44:57,320 This ancient people disappeared in the 7th century, 656 00:44:57,480 --> 00:44:59,880 prompting the fall of this superb city. 657 00:45:00,040 --> 00:45:03,560 Why did the citizens of this prosperous and busy city 658 00:45:03,720 --> 00:45:05,560 abandon Petra and flee? 659 00:45:12,160 --> 00:45:14,560 There was an economic decline. 660 00:45:15,600 --> 00:45:19,840 The cause of Petra's lost status can be traced 500 kilometres away 661 00:45:20,000 --> 00:45:23,840 to the city of Palmyra's rising economic importance. 662 00:45:24,000 --> 00:45:26,800 But another disaster played a role, too. 663 00:45:26,960 --> 00:45:31,800 The big turning point, when damage started again 664 00:45:31,960 --> 00:45:35,280 was definitely the earthquake of 363 AD. 665 00:45:36,640 --> 00:45:38,800 All the water system, the cisterns 666 00:45:38,960 --> 00:45:41,440 and the aqueducts were damaged heavily, 667 00:45:41,600 --> 00:45:44,840 and were not, no longer reconstructed in the future. 668 00:45:46,480 --> 00:45:49,240 The ending of Petra, it will finally come 669 00:45:49,400 --> 00:45:51,960 when they no longer maintained those water access points. 670 00:45:52,120 --> 00:45:54,200 There is not enough rainfall there 671 00:45:54,360 --> 00:45:56,920 to sustain agriculture on a normal basis. 672 00:45:59,520 --> 00:46:03,160 Even the ingenious anti-seismic measures of the Nabataeans 673 00:46:03,320 --> 00:46:05,600 weren't enough to save the city from destruction. 674 00:46:06,560 --> 00:46:09,520 But some scientists have suggested another theory - 675 00:46:09,680 --> 00:46:13,600 that in 400 A.D. the city fell victim to a different tragedy. 676 00:46:15,200 --> 00:46:17,920 By analysing the ground of the town's main road, 677 00:46:18,080 --> 00:46:21,040 they discovered the presence of unusual white sand, 678 00:46:21,200 --> 00:46:24,800 totally different to the local red or orange sand. 679 00:46:24,960 --> 00:46:29,080 There was a very irregular event 680 00:46:29,240 --> 00:46:34,360 which deposited white sand in amongst the buildings of Petra. 681 00:46:34,520 --> 00:46:36,000 And that could only have come 682 00:46:36,160 --> 00:46:39,880 from an area some distance away from Petra. 683 00:46:40,040 --> 00:46:44,240 So it was a monumental flood which happened 684 00:46:44,400 --> 00:46:49,800 and it could well have destroyed the entire population 685 00:46:49,960 --> 00:46:51,840 certainly in the centre of the city. 686 00:46:52,840 --> 00:46:55,040 But today this theory is disputed 687 00:46:55,200 --> 00:46:57,920 because signs of life and even subsequent building work 688 00:46:58,080 --> 00:46:59,880 have been discovered in Petra. 689 00:47:09,720 --> 00:47:11,920 So life went on 690 00:47:12,080 --> 00:47:15,400 but it did not go on 691 00:47:15,560 --> 00:47:19,520 as rich or as strong as before. 692 00:47:24,120 --> 00:47:26,760 These Byzantine churches, with their famous mosaics, 693 00:47:26,920 --> 00:47:29,760 are the final, glorious chapter of a city 694 00:47:29,920 --> 00:47:34,360 which is thought to have finally sunk into oblivion in the 7th century A.D. 695 00:47:34,520 --> 00:47:37,560 The lost city of Petra was only rediscovered 696 00:47:37,720 --> 00:47:41,680 in the beginning of the 19th century by a Swiss explorer. 697 00:47:41,840 --> 00:47:43,600 Since then, this marvel of architecture 698 00:47:43,760 --> 00:47:47,560 has been observed from every angle and on every scale 699 00:47:47,720 --> 00:47:49,760 by hundreds of scientific missions, 700 00:47:49,920 --> 00:47:52,480 revealing new parts of the city's history. 701 00:48:10,080 --> 00:48:11,960 We only have glimpses of the Nabateans, 702 00:48:12,120 --> 00:48:17,040 we only have glimpses of their glorious city, capital city. 703 00:48:18,760 --> 00:48:22,080 Piece by piece, the secrets of this city's construction 704 00:48:22,240 --> 00:48:25,800 have been revealed though meticulous work on all scales. 705 00:48:25,960 --> 00:48:28,920 But mysteries still endure. 706 00:48:29,080 --> 00:48:32,200 So for now, this pink city of the desert 707 00:48:32,360 --> 00:48:35,480 will remain the perfect playground for archaeologists, 708 00:48:35,640 --> 00:48:38,120 architects and hydraulic engineers, 709 00:48:38,280 --> 00:48:42,240 all passionate about the incredible heritage left by the Nabataeans.