The city itself, like everything in Jordan, is ancient, the name comes from the Latin saltus - forest. But the real prosperity of the city took place at the turn of the 19th and 20th centuries, when the administrative regional center of the Ottoman Empire was located here, and even the independence of Transjordan was declared here in 1922 (but the center of power moved to neighboring Amman later). In order to receive an UNESCO status, As-Salt is presented as a place of peaceful and harmonious coexistence of different religions, because in addition to the Great Mosque, there is also a Latin church, two Orthodox churches, and even an Anglican hospital. It is strongly suspected that the main motive behind the nomination by Jordan was that this city, as the first capital, has a special significance for Jordanian history.
In the tourist center, you can take a booklet with the "route of harmony", which gives at least some sense of place when exploring the city. But I hoped that the Ottoman architecture of the "capital period" would be more interesting, it is modest actually. In fact, it is a suburb of Amman now, so it is easy to get here by car.