When the news about the approaching army of the
First Crusade reached Antioch, Yağısıyan whose army of 6,000 was no match for the Crusaders and he tried to form a united front to defend Antioch. But because of jealousies between the Seljuk governors and the anarchy in the main sultanate after the death of Malik-Shah, he got very little support. Sökmen, whose principality was far to the east and far from the crusades' route, refused to assist Yağısıyan. Even Ridwan, whose domain was next to Antioch, sent only a small number of troops. According to
David Nicolle, mistrust between Yağısiyan and Ridwan influenced the First Crusade. Over the winter of 1097–98,
Antioch was besieged by the Crusaders, and Yağısiyan sought help from Duqaq. He frequently sent out sorties against the Christian camp and attacked foraging parties further afield. Yağısiyan knew from his informants that there were dissensions among the Christians; both
Raymond IV of Toulouse and
Bohemund of Taranto wanted the city for themselves. While Bohemund was away foraging on 29 December 1097, Raymond attacked but was pushed back by Yağısiyan's troops. On 30 December reinforcements from Duqaq were defeated by Bohemund's foraging party and retreated to
Homs. Only after the beginning of the siege did Ridwan decide to leave Aleppo and challenge the crusaders. Ridwan's army was defeated in the
Battle of the Lake of Antioch on 8–9 February 1098. While the crusader army was away from the city fighting Ridwan, Yağısiyan marched out to attack the foot-soldiers left behind to defend the camp, but he too was pushed back when the victorious crusaders returned. In March Yağısiyan ambushed the crusaders who were bringing wood and other material back from the port of St. Simeon; when the crusader camp at Antioch heard that Raymond and Bohemund had been killed, there was mass confusion, and Yağısiyan attacked the rest of the army under
Godfrey of Bouillon. Bohemund and Raymond soon returned and Yağısiyan was once more pushed back into the city. At this time the governor turned to
Kerbogha, the
atabeg of
Mosul for help. The crusaders knew they had to take the city before Kerbogha's reinforcements arrived. Bohemund secretly negotiated with one of Yağısiyan's guards, an
Armenian convert named
Firouz, and on 3 June he helped Bohemund's men to open the gates of the city to crusaders. ==Death==