Petra

30.3285°N, 35.4444°E.

Nabataean caravan city in southern Jordan, occupied from approximately the 4th century BCE through the 7th century CE. The city was carved directly into the red sandstone cliffs of the Wadi Musa; principal façades — the Khazneh (Treasury), the Monastery, and the Royal Tombs — were carved top-down from solid rock, eliminating the possibility of structural failure during construction. The Khazneh stands 39.6 metres tall and was carved approximately the 1st century BCE. Petra controlled the incense trade routes from southern Arabia to the Mediterranean; population peak estimated at 20,000–30,000. A sophisticated water system collected runoff from over 200 cisterns and channels covering 90 km² of catchment — keeping the city green in a region receiving 150 mm of annual rainfall. Petra was forgotten by Europeans after the Crusades and rediscovered by Swiss explorer Johann Burckhardt in 1812.

A city of 30,000 was carved out of solid sandstone in a desert receiving less rain than the Sahara — and Europe forgot it existed for 600 years.