The Catarans are the outcasts of the Sali civilization. Over a hundred years ago, a holy man amoungst the Sali named Zaurac 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. Zaurac claimed that each spirit also had a human counterpart needed to become more perfect.
This culminated, eventually, 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 Sali worshiped. This perfect, immortal being would usher in a new golden age, fully combining the world of spirits with the physical world. This idea was, and is, extremely offensive to the more religious members of the Sali .
After being cast out, they roamed the desert for 13 years, and it became 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, following the original path of the exiled Catarans, and 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 Sali and the Catarans to be where the all-powerful spirit they worship lives. The city takes 13 years to complete it's path, mirroring the 13 years that it took for Zaurac to return to the holy mountain Raheem.
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.