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Map of Roman Palestine with the Decapolis cities (which includes Gerasa) labeled in red.

Jerash (ancient "Antioch-on-the-Chrysorhoas", also known as Gerasa) was a city of the Graceo-Roman Decapolis, its ruins now located in the Gilead region of northwest Jordan.

The origins of the city are in the Iron Age and even a Bronze Age predecessor. The Graceo-Roman originated in the 2nd century BC; after 63 BC it was a city of the Roman Empire. Initially it was part of the province of Syria but in AD 106 the Romans annexed the Nabataean kingdom and created a new province called Arabia and including both Gerasa and Philadelphia (modern Amman).

The city finally reached a size of about 800,000 square metres within its walls. The site was largely abandonned from the 12th century until a small Circassian settlement was established in the late 19th century. The result has been survival of spectacular ruins. Excavation and restoration has been almost continuous since the 1920s.

There are a large number of striking monuments: Hadrian's Arch, a circus/ hippodrome, two immense temples (to Zeus and Artemis), the nearly unique Oval Piazza with a fine colonnade around it, a long colonnaded street, two theatres (the Large South Theatre and smaller North Theatre), two baths, a scatter of small temples and an almost complete circuit of city walls. In its later history, Christianity came to dominate religion and is represented by at least 14 churches, many with superb mosaic floors.

A key moment in its history would have been the visit by the Emperor Hadrian (AD 117-138) in 127-128. A remarkable Latin inscription records a religious dedication set up by members of the imperial mounted bodyguard "wintering" there. Soon after, a local worthy paid for the construction of the great Arch of Hadrian on the south side of the city on the road coming in from Philadelphia (Amman).

Today the ruins of Jerash are thoroughly excavated and excellently preserved. This has led to a nickname, the "Asian Pompeii."

Modern Jerash sprawls to the east of the ruins, sharing the same city wall but little else. The ruins have been carefully preserved and spared from encroachment. Due to the ruins, Jerash is the second-most popular tourist attraction in Jordan, closely behind the splendid ruins of Petra.