The siege of Nicaea was the first major battle of the
Seljuk Turks who opted to surrender to the Byzantines in fear of the crusaders breaking into the city. The siege was followed by the Battle of Dorylaeum and the Siege of Antioch, all taking place in modern Turkey.[4][5]
Robert II of Flanders following him, along with Peter the Hermit and some of the survivors of the People's Crusade, and a small Byzantine force under Manuel Boutoumites. They arrived on 6 May, severely short of food, but Bohemond arranged for food to be brought by land and by sea. The crusaders put the city to siege beginning on 14 May, assigning their forces to different sections of the walls, which was well-defended with 200 towers and sent a message to Raymond to hurry his advance to aid the siege. Bohemond camped on the north side of the city, Godfrey on the south, and Raymond and Adhemar of Le Puy
on the eastern gate.
Defeat of Kilij Arslan
On 16 May the Turkish defenders sallied out to attack the crusaders, but the Turks were defeated in a skirmish with the loss of 200 men. The Turks sent messages to Kilij Arslan begging him to return, and when he realized the strength of the crusaders he quickly turned back. An advance party was defeated by troops under Raymond and Robert II of Flanders on 20 May, and on 21 May the crusader army defeated Kilij in a pitched battle which lasted long into the night. Losses were heavy on both sides, but in the end the sultan retreated despite the pleas of the Nicaean Turks. The rest of the crusaders arrived throughout the rest of May, with
arriving at the beginning of June. Meanwhile, Raymond and Adhemar built a large siege engine, which was rolled up to the Gonatas Tower in order to engage the defenders on the walls while miners mined the tower from below. The tower was damaged but no further progress was made.