Kotyaion (modern Kütahya) is city of Phrygia at a strategic road junction. It is the site of an exceptionally powerful fortress. A city of the Opimon theme, Kotyaion occasionally appears in history as a place of refuge or exile; Romanos IV was blinded there in 1072. The Byzantines lost it around 1082, but recovered it for a brief while. A suffragan bishopric of Synnada, Kotyaion was made metropolis in the early 9th century. It rose to greater prominence after its recapture by the Seljuks in 1182 or 1183. The extensive fortifications of Kotyaion, with more than 70 towers, are well preserved. Their first stage, of the early 9th century, consisted of a double wall that made extensive use of spolia. This was replaced by more massive structures of ashlar with bands of brick, apparently of the 12th century. No other Byzantine remains survive.
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Oxford Dictionary of Byzantium