In 1812 the Swiss traveler Johann Ludwig Burckhardt, disguised as a local and leading a goat to sacrifice at the tomb of Aaron, walked through the narrow Siq and into Petra. The basin gets only about 7.6 inches of rain a year, yet it was settled by Neolithic farmers at Beidha around 7000 BC and later by the Edomites. In the fourth century BC the Nabataeans, a nomadic Arab tribe, made it their city of Raqmu, a choke point on incense routes linking Gaza, Damascus, and the Persian Gulf. They dammed the flash floods, cut a 280 foot tunnel to send the water around the city, and ran ceramic pipes at a steady four degree slope to feed cisterns and sell water to caravans.

The wealth went into rock-cut monuments like the 121 foot Treasury, an 8,500 seat theater, and a garden with a public swimming pool. Rome annexed the kingdom in 106 AD as Arabia Petraea, and under Byzantine rule the Urn Tomb became a church. More than 140 carbonized papyri from a sixth century church show a family around the archdeacon Theodoros suing over property and inheritances as the incense trade moved to the Red Sea. The earthquake of 363 broke the water system, and the city emptied. The Bdoul Bedouin lived in the tombs until they were relocated in the 1980s, and after its 2007 New Seven Wonders listing Petra passed one million visitors in 2019.

• Why nomadic knowledge of desert water made the Nabataeans skilled hydraulic engineers
• Bullet holes in the Treasury’s stone urn from Bedouin who believed a pharaoh’s gold was hidden inside
• Castor and Pollux, Egyptian obelisks, and the goddess Isis-Tyche on the facades as signals to foreign merchants
• Salt weathering, where moisture from millions of visitors crystallizes salt that flakes the carvings away
• An Olympic stadium-sized platform half a mile south of the city center, spotted by satellite and drones in 2016