Recent excavations show that Jerash was already inhabited during the Bronze Age (3200 BCE - 1200 BCE). After the Roman conquest in 63 BC; Jerash and the land surrounding it were annexed by the Roman province of Syria; and later joined the Decapolis cities. In 90 CE; Jerash was absorbed into the Roman province of Arabia; which included the city of Philadelphia (modern day Amman). 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. In the second half of the first century CE; the city of Jerash achieved great prosperity. In 106 CE; the Emperor Trajan constructed roads throughout the provinces and more trade came to Jerash. The Emperor Hadrian visited Jerash in 129-130 CE. The triumphal arch (or Arch of Hadrian) was built to celebrate his visit.

The city finally reached a size of about 800;000 square metres within its walls. The Persian invasion in 614 CE caused the rapid decline of Jerash. However; the city continued to flourish during the Umayyad Period; as shown by recent excavations. In 749 CE; a major earthquake destroyed much of Jerash and its surroundings. During the period of the Crusades; some of the monuments were converted to fortresses; including the Temple of Artemis. Small settlements continued in Jerash during the Ayyubid; Mameluk and Ottoman periods. Excavation and restoration of Jerash has been almost continuous since the 1920s.