THILUTHA an impregnable fortress on an island in the Euphrates, near Anatho, which defied the arms of Julian (Ammian. 24.2). Zosimus (3.15) speaks of this island, and of the impregnable fortress (φρούριον ὀχυρώτατον) situated upon it, but without mentioning its name. It is described by Isidorus Charax ( Mans. Parth. § 1, ed. C. Müller) as an island in the Euphrates, containing a treasury of the Parthians, and distant two schoeni from Anatho. The old editions read Ὀλαβούς;but the MSS. have Ὁλαβούς, which Müller has changed into Θιλαβούς, and there can be little doubt of the propriety of this correction. It corresponds to the island called Tilbusby Chesney (vol. 1. p. 57), and in his map Telbesor Anatelbes, containing ruins of very ancient buildings. (See Müller, ad Isid. Char. l. c. ）