Until its annexation by Rome in 106 A.D., Petra served as a capital for the Nabataeans, a people who wrote using an Aramaic language and controlled caravan trade throughout the region. The earliest mention of these people is from 312 B.C., when they apparently withstood an assault by Antigonus, one of Alexander the Great's successors. In these early years the Nabataeans are believed to have lived a nomadic lifestyle, and Petra was likely a place of tents and simple structures. This would change as the caravan trade developed, with Petra serving as a center of trade between Arabia, Mesopotamia, Egypt and the eastern Mediterranean. The city reached its peak about 2,000 years ago with a population estimated at 20,000 inhabitants.