Cevirian, Thrax Is a Prison, Right?

Based on Cevirian's descriptions, Thrax is most easily breached by treachery because it's located basically right in the town. But at the same time he's upholding the citadel as the better example of this, even though it falls prey to the very weaknesses or problems that he enumerates. Despite the fact that he's in charge of it, he is held in Thrax. There is no way that he could get out of this easily.