In ancient times the area of Jerash was known as Gerasa. It is located on the banks of the river Chrysorhoas, about 42 km north of modern Amman Jordan. The site has been occupied from the 3000 BC. From the 8 - 7th century BC the area was settled by Semetic people who worshiped Baal. From the 7th century until the 300 BC the site was abandoned and visited only by nomadic Nabataeans.
When Alexander the Great conquered the area in 334 BC Gerasa became a Macedonian Greek colony. In 301 BC the Ptolemaic kingdom annexed the area but later lost it to the Seleucids. Under Selucid control the area was thoroughly Hellenized and a number of towns sprang up along the Nabataean caravan route that passed nearby linking Petra with Damascus. It was during this time that the city proper was developed. The city changed its name to Antiochia on the Chrysorhoas or Antiochia of the Gerasenes, after the Selucid king, (Antiochus III or IV) decreed that the city be refounded in his name.
When the Romans conquered the area in 63 BC the city became known as Gerasa of the Decapolis, a group of ten cities that made up a small Roman province. Economic prosperity was experienced between the end of the 1st century BC and the 1st century AD. The historian Josephus regarded it as one of the most important cities in the Decapolis. A number of grand public buildings were built during this period.
During the Jewish Revolt of 66 AD seemed to have little effect on the city, although it is said that Lucius Annius led a military expedition against the city in 67 AD. Later under the emperor Trajan (106 AD) there was a political reorganization of the region, as the neighboring Nabataean empire was absorbed into the Roman Empire. The Roman province of the Decapolis ceased to exist, and the Province of Arabia was formed.
Under the new provincial system the city of Gerasa prospered further, especially as the Roman road known as the Via Nova Traiana passed by the city. This city linking Aqaba and Petra in the south with Basra and Damascus in the north.
Later in 129 - 130 AD the city gained more public buildings in preparation for the visit of the emperor Hadrain. A three door ceremonial arch was put up in Hadrain’s honor. Later in the second half on the 2nd century AD the Temple of Artemis, the city’s patron deity was re-built. In the 3rd century AD, Caracalla awarded it the title ‘Colonia Aurelia Antoniniana.’ Shortly after this the city started to decline due to the expansion of the Sassanid Persians from the east.
Between the 4th and 6 centuries, there was some economic renewal in the area, and Gerasa became an important Christian center. During this time some 15 churches were built in the urban area. The oldest church was the Church of Saint Theodore, which later became part of the Gerasa cathedral. The Propylaea of the Sanctuary of Artemis was converted into a church. Most of the churches, (Saint Cosmas and Damian, Saint George and Saint John) date to the time of Justinian (527-565 AD).
The city was still active in the 7th and 8th centuries AD, but it was probably destroyed in an earthquake in 746 - 747 AD.