What is this strange city carved into the sandstone hills of Southern Jordan? How could such a civilisation suvive for so many years in an almost desert environment? In the third century BC Edom became the centre of an Arab state, the Nabatean Kingdom. Petra was the capital. Over time a highly developed system of water-harvesting channels and reservoirs was created. Water collected during the winter as well as several fresh-water springs enabled the growing civilisation to survive during the long summer. Petra is situated close to North-South and East-West trade routes and the Nabateans were able to become wealthy through contol of the trade. Petra was a loyal ally of Rome during the first century BC and the first century AD, but began to go into decline as the Romans began to divert trade to its own ports on the Egyptian side of the Red Sea. It remained a bishopric in the Byzantine era and was finally abandoned as a major city in the early Islamic period.