After the Roman conquest in 63 BC, Jerash and the land surrounding it were annexed to the Roman province of Syria, and later joined the Decapolis league of cities. The historian Josephus mentions the city as being principally inhabited by Syrians, and also having a small Jewish community. In AD 106, Jerash was absorbed into the Roman province of Arabia, which included the cities of Philadelphia (modern day Amman), Petra and Bostra. The Romans ensured security and peace in this area, which enabled its people to devote their efforts and time to economic development and encouraged civic building activity.