Yağısıyan, also known as Yaghi-Siyan (Turkish pronunciation: [ˈyaːɯsɯjan]; died 1098) was a Seljuk Turkoman commander and governor of Antioch in the 11th century.
[2] Malik-Shah I died in 1092, and his brother at Damascus, Tutush I, granted Yağısiyan more territory around Manbij and Turbessel.
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.
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.
On the night of June 3, 1098, the crusaders entered the city; Yağısiyan fled with his bodyguard, while his son Shams ad-Daulah stayed behind to defend the citadel.
During his escape, Yağısiyan fell from his horse, and as his guards found it impossible to bring the injured governor with them, they left him on the ground and rode away without him.
However, Bohemund finally won out the argument, and thus declared the creation of the Principality of Antioch, which went on to exist for another 170 years.
The crusaders recorded Yağısiyan's name in various forms in Latin, including Acxianus, Gratianus, and Cassianus; the residence claimed by Raymond was known as the palatium Cassiani.