Battle of Nicaea

From May 14 to June 19, 1097, the armies of the First Crusade surrounded Nicaea, capital of Kilij Arslan. The French contingents, led by Godfrey of Bouillon, Raymond of Saint-Gilles and Bohémond, established countervallation lines while the Byzantine fleet of Manuel Boutoumites locked Lake Askania. The repeated assaults on the walls, combined with the failed return of Kilij Arslan, led to the negotiated capitulation of the garrison for the benefit of the Byzantine Empire.

Nicaea controls access to western Anatolia. Western chroniclers underline the latent rivalry between crusader leaders and Byzantine officers, because Alexios I Comnenus wanted to recover the city intact. Kilij Arslan, on campaign against the Danichmends, underestimated the Frankish threat and only returned after the siege had been completely installed. The Crusaders built wooden towers, battering rams and throwing machines, while repelling several Seljuk sorties. Outcome: Nicaea restored to the Byzantine Empire, not crusader-sacked (English Wikipedia). Lasting crusader / Alexios I tension.

The siege opened on 14 May 1097, the first contingents having arrived around 6 May. The crusaders deployed around the city: Bohemond to the north, Godfrey of Bouillon to the south, Raymond of Saint-Gilles and Adhemar of Le Puy to the east. They repulsed a sortie by the garrison on 16 May, then a relief attempt by Kilij Arslan on 20-21 May. A siege engine set against the Gonatas tower, together with mining, damaged the work without opening a breach. Lake Ascanius supplied the city until 17 June, when Byzantine boats hauled overland under Manuel Boutoumites closed that access, supported by two thousand men under Tatikios. Alexios I then secretly negotiated a surrender to his own benefit: the city yielded to the Byzantines on 19 June, entry was limited to ten crusaders at a time and looting forbidden, to the army's considerable anger. The leaders swore fealty, and the army left on 26 June in two columns for Dorylaeum, reached on 1 July.

The surrender orchestrated by Boutoumites, who raised the imperial standard before those of the crusaders, caused an initial friction between allies but ensured the restitution of Nicaea to Byzantium. The crusaders received provisions, pay and guides there, then set off again towards the Anatolian interior. Kilij Arslan, humiliated, reorganizes his forces to prepare the ambush of Dorylaeus.