Catarans

The Catarans are the outcasts of the Sila civilization. Over a hundred years ago, a holy man amoungst the Sila claimed that humans and spirits were part of a greater whole, and that one must a personal spirit and bind with it permanently to become a more perfect being. His small cult gained some traction, and for a number of reasons, they were banished and cast out. The princes of the local cities feared their growing influence and magical abilities, and the populace were offended by the religious implications. The teachings offended them because the prophet also preached that each spirit had a human counterpart that it needed to become more perfect.

This culminated in a messianic prophecy stating that a human would one day be born which was the counterpart to the great spirit-above-all that the Sila worshiped. 

After being cast out, they roamed the desert for many years, keeping it as a tenant of their faith that the search for their partner spirit must be physical as well as spiritual. Eventually, they managed, with the help of a powerful spirit, to construct one of the great marvels of the world: Catar, the Roaming City. The city roams the desert wastes, acting as a way-point for pilgrims, and as the seat of both governmental and spiritual power for the Catarans. 

When the city nears another large settlement, especially near the edge of the desert, it is always an occassion for great excitement, for a large number of people always brings with it a large amount of trade, but the most important stop on it's route is the sacred mountain at the edge of the desert. (This probably needs a name.) Beleived by both the Sila/Sojo and the Catarans to be where the all-powerful spirit they worship lives. The city follows a set path, taking several years to complete it's path, governed in part by a powerful spirit, that takes several years to work it's way across the desert, through dozens of holy and spiritually-active sites and back again.

Outside of Catar, there are at least a few Catarans to be found in just about every major city in the world. Many Catarans travel the world seeking out their companion spirit, finding some reason to beleive that it is not to be found in the desert. Their pilgramidges take them all over the world, and it's not unusual to find a few Cataran adventurers willing to explore new places.