Zarqa is the second populated city after Amman. As early as the nineteenth century, refugees from the Caspian Sea settled on the banks of the Zarqa River, and the city grew especially after when an Army Camp and Palestinian 1948 refugee camp were established there. During the construction of the Hijaz railway, the Zarqa station on the Hajj route was built. The line from Amman to Zarqa to Damascus is still functional especially for cargo transport. The city grew randomly into a highly populated traffic congested urban centre. Its western part is more modern with stone clad houses similar to those in Amman.