[4][5] Nicaea, located on the eastern shore of Lake Askania, had been captured from the Byzantine Empire by the Seljuk Turks in 1081, and formed the capital of the Sultanate of Rûm.

Bohemond camped on the north side of the city, Godfrey on the south, and Raymond and Adhemar of Le Puy on the eastern gate.

The Turks sent messages to Kilij Arslan begging him to return, and when he realized the strength of the crusaders he quickly turned back.

Byzantine emperor Alexios I chose not to accompany the crusaders, but marched out behind them and made his camp at nearby Pelecanum.

From there, he sent boats, rolled over the land, to help the crusaders blockade Lake Ascanius, which had up to this point been used by the Turks to supply Nicaea with food.

Boutoumites, however, was named dux of Nicaea and forbade the crusaders from entering in groups larger than 10 men at a time.

The crusaders left Nicaea on 26 June in two contingents: Bohemond, Tancred, Robert II of Flanders, and Tatikios in the vanguard, and Godfrey, Baldwin of Boulogne, Stephen, and Hugh of Vermandois in the rear.