Situated between the Red Sea and the Dead Sea and inhabited since prehistoric times, the rock-cut capital city of the Nabateans, became during Hellenistic and Roman times a major caravan centre for the incense of Arabia, the silks of China and the spices of India, a crossroads between Arabia, Egypt and Syria-Phoenicia. Petra is half-built, half-carved into the rock, and is surrounded by mountains riddled with passages and gorges. An ingenious water management system allowed extensive settlement of an essentially arid area during the Nabataean, Roman and Byzantine periods. It is one of the world's richest and largest archaeological sites set in a dominating red sandstone landscape. The Outstanding Universal Value of Petra resides in the vast extent of elaborate tomb and temple architecture; religious high places; the remnant channels, tunnels and diversion dams that combined with a vast network of cisterns and reservoirs which controlled and conserved seasonal rains, and the extensive archaeological remains including of copper mining, temples, churches and other public buildings. The fusion of Hellenistic architectural facades with traditional Nabataean rock-cut temple/tombs including the Khasneh, the Urn Tomb, the Palace Tomb, the Corinthian Tomb and the Deir ("monastery") represents a unique artistic achievement and an outstanding architectural ensemble of the first centuries BC to AD. The varied archaeological remains and architectural monuments from prehistoric times to the medieval periods bear exceptional testimony to the now lost civilisations which succeeded each other at the site.