The siege of Cotyaeum was the successful capture of the city by Seljuk Turk forces from the Byzantines.
Following Emperor Manuel Komnenos' defeat at Myriokephalon, the Byzantines failed to reconquer any more territory. With Manuel's death in 1180 the leadership passed to his young son Alexios II Komnenos and an incompetent regency cursed with an obsession for Western culture (which led to its demise). With such a weak government, numerous cities fell, including Cotyaeum (Turkish: Kütahya) and Sozopolis.
The capture of the city did not lead to a peace. Instead Andronikos Komnenos would overthrow Alexios II and attempt to revive Manuel's successful policies until Isaac Angelus came to terms with the Sultan.