Petra achieved its greatest importance under the Nabateans, an ancient people whose original homeland was in northeastern Arabia. They migrated westward in the 6th century BC and eventually settled at Petra. Little is known about the Nabateans' history before 312 BC, when Petra was unsuccessfully attacked by Seleucid forces. The High Place of Sacrifice was probably built during this time. As the Seleucid kingdom weakened in the 2nd century BC, the Nabataean kingdom increased in strength. The chief source of the Nabataeans' prosperity and power was their monopoly on the caravan spice trade that involved such distant places as China, Egypt, Greece, India and passed from the Arabian interior to the coast.
By the 1st century BC the rich and powerful Nabataean kingdom that extended from Damascus in the north to the Red Sea in the south, and Petra was home to as many as 30,000 people. It was during this period that the most impressive structures of Petra were built, including the Treasury, the Great Temple and the Qasr al-Bint al-Faroun.
A significant key to the city's success was the Nabataeans' ability to control and conserve water. Conduits and the remains of terracotta piping can be seen along the walls of the Outer Siq, which was part of an elaborate system for channelling water around the city.
