The Siege of Nicaea took place from May 14 to June 19, 1097, during the First Crusade.
Nicaea, located on the eastern shore of Lake Ascanius, had been captured from the Byzantine Empire by the Seljuk Turks in 1077, and formed the capital of the Sultanate of Rüm. In 1096, the People's Crusade, the first stage of the First Crusade, had plundered the land surrounding the city, before being destroyed by the Turks. As a result, Sultan Kilij Arslan I initially felt that the second wave of crusaders were not a threat. He left his family and his treasury behind in Nicaea and went east to fight the Danishmends for control of the Melitene.