Under Ptolemy II Philadelphos (285-247 B.C.), Amman was rebuilt and renamed Philadelphia. In 63 B.C., Philadelphia became part of the Decapolis set up by Pompey. In 106 A.D., Philadelphia was included in the Roman province of Arabia by the Emperor Trajan. He built a new road from Elath to Damascus which ran through Philadelphia. This created an economic boom for the city and it flourished. Most of the town's Roman structures were built in the 2nd century A.D., including the theater, forum and Hercules temple.
Read more at http://www.bibleplaces.com/amman.htm