Thrax itself is clearly a fortress city. Such a place could scarcely be expected to stand for more than a day at most against the Ascian enemy — rather, it seems designed to fend off raids by brigands and rebellions by the local exultants and armigers. (Cyriaca’s husband, who would have been a person almost beneath notice in the House Absolute, is clearly of some importance, and even some danger, in the neighborhood of Thrax.) Although the exultants and armigers seem to be forbidden private armies, there appears little doubt that many of their followers, though called huntsmen, stewards, and the like, are fundamentally fighting men. They are presumably essential to protect the villas from marauders and to collect rents, but in the event of civil unrest they would be a potent source of danger to such as Abdiesus. The fortified city straddling the headwaters of the river would give him an almost irresistible advantage in any such conflict.

The route chosen by Severian for his escape indicates how closely egress from the city could be controlled. The archon’s own fortress, Acies Castle (“the armed camp of the point”), guards the northern end of the valley. It appears to be entirely separate from his palace in the city proper. The southern end is closed by the Capulus (“the sword haft”), apparently an elaborate fortified wall, a scaled-down imitation of the Wall of Nessus. Even the cliff tops are protected by forts linked by walls. Possessing, as it does, an inexhaustible supply of fresh water, the city appears capable of withstanding a protracted siege by any force not provided with heavy armament.