Castle Pass has been granted as a fief by the Dukes of Thranconia to the Order of the Invincible Sun, a religious order of knights in service to the god Mithras. The knights hold the castle in exchange for keeping the pass open and travelers safe along the road.

In addition to the barracks, armories and stables of the knights, there is a large temple of Mithras with its own High Priest. The order is ruled by a Grand Master chosen by the knights at the death or retirement of the previous one. While the High Priest has much influence among the knights, the Grand Master rules the order and the castle.