Ducas. Hist. c. 34 [p. 136, ed. Paris; p. 108 ed. Ven.; p. 242, ed. Bonn]. Leunclavius Hist. Turcica Mussulmanica, 1. xv. p. 577. Under the Greek empire these castles were used as state prisons, under the tremendous name of Lethe, or towers of oblivion.