This slim notebook, written throughout in French and attributed to the scholar-explorer Petrus Gyllius, is signed in every margin with the initials "PG." It was drawn up sealed and dry from a waterproof metal box laid away beneath a cistern, and its pages prove the record of a curious and methodical mind: charts, drawings, and patient explanations of architecture and of the mechanisms by which water is moved from one place to another. The diary speaks of a stair descending below the cistern; it sets down the author's belief that Justinian was wont to dispose of the bodies of magic-users in the depths beneath it; it makes mention of a huge cage, of travels undertaken in the company of fellow members of the lodge, and — in a phrase that lingers — of a "dreaded she-devil."
It was Jean-Zera who first knew the hand, recognising a French carving signed with that same "PG," and who, once the sealed box was brought up, read the diary through. Its entries were studied at leisure during a rest, and set beside a close reading of the masonry; between the two, the company were able to date the prison complex to the age of Justinian.