Jerash is known for the ruins of the Greco-Roman city of Gerasa, also referred to as Antioch on the Golden River. It is sometimes misleadingly referred to as the "Pompeii of the Middle East or Asia", referring to its size, extent of excavation and level of preservation (though Jerash was never buried by a volcano). Jerash is considered one of the most important and best preserved Roman cities in the Near East. It was a city of the Decapolis. Jerash was the home of Nicomachus of Gerasa who is known for his works Introduction to Arithmetic (Arithmetike eisagoge), The Manual of Harmonics and The Theology of Numbers. Recent excavations show that Jerash was already inhabited during the Bronze Age (3200 BC to 1200 BC). 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 AD 90, 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 AD, the city of Jerash achieved great prosperity. In AD 106, the Emperor Trajan constructed roads throughout the provinces and more trade came to Jerash. The Emperor Hadrian visited Jerash in AD 129-130. The triumphal arch (or Arch of Hadrian) was built to celebrate his visit. A remarkable Latin inscription records a religious dedication set up by members of the imperial mounted bodyguard "wintering" there. The city finally reached a size of about 800,000 square metres within its walls. The Persian invasion in AD 614 caused the rapid decline of Jerash. However, the city continued to flourish during the Umayyad Period, as shown by recent excavations. In AD 749, 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.