As-Salt, the capital of the Balqa' region, has attracted settlers since before the Iron Age, mainly due to the fact that the area enjoys a moderate climate, a plentiful supply of water and fertile soil. The town was also well placed on the north to south trade routes and those running from east to west, linking the interior with Jerusalem, Nablus, Nazareth and the Mediterranean coast. As-Salt’s mixed Muslim-Christian population and its centuries-old trading connections has helped create the town’s enviable reputation for ethnic and religious tolerance and coexistence.
Evidence of the Roman times can still be seen and there are several Roman tombs on the outskirts of the town. During the Byzantine period the town was known as Saltos, which means forest/wooded trees. In the Byzantine period the town was known as Jadaron/Jader and it was depicted on a mosaic pavement from Ma’in where it is labeled “ Jadaron.” In the 13th century an Ayyubid fortress was built on the site of the citadel by the Sultan Al Mu'azzam Isa (a nephew of Saladin), who was based in Damascus. The fortress was destroyed by invading Mongols in 1260, but was rebuilt a year later by a second Mameluk ruler from Egypt. Six centuries later, in 1840, the forces of yet another Egyptian potentate, Ibrahim Pasha, demolished it yet again. The citadel is now the site of a large mosque, which towers over the modern town.
By the early 19th century, As-Salt was a prosperous frontier town on the edge of the Ottoman Empire and the desert. Useful to all, it was ruled by none and the people of As-Salt were said to be "free from taxation of any kind." The town was also the center of lucrative trading between the region and urban centers in Palestine.
The town's fortunes and status declined after World War I, when Emir Abdullah ibn Al-Hussein chose Amman to be the capital of the new Emirate of Transjordan.