Of all the spellcasters in Rothganar, the most revered were the Magi of Dixon Forest. Very few priests and almost no shamans ever took one of the six towers, two each for white, gray, and black. White represented good casters, black evil, and gray neutral.
Casters in white towers were traditionally chosen and educated by their predecessors. As one might imagine, this presented problems if the caster who owned the tower misjudged matters, and after three Magi in a row were killed by their apprentices, the others instituted a complex ritual by which prospective White Magi might be tested.The details of this ritual were shrouded in secrecy, particularly since it was impossible by magic to tell what any one person might do.
Casters inhabiting gray towers were called to their places when the previous Gray Magus died. The towers themselves would reach out to the nearest suitable candidate to come and take up residence; if the candidate chose to reject the calling, the tower would move to the next.
Casters of black magic were presented with perhaps the most difficult test. When a Black Magus died (or was killed), the tower would issue a general call, and wicked casters would converge on its location and fight for possession of the tower. As you can imagine, the towers of the black changed hands often, and only the exceedingly clever or powerful could hold one for long.
These six casters were considered the finest and most powerful in the world, particularly the two Gray Magi, who were chosen by their towers based on skill and dedication to study above all else. The magical libraries of the gray were famous all over the planet for their size and the breadth and depth of occult knowledge contained therein.