埃德萨伯国
The Fortress of Kaysun () is located near the village of Çakırhüyük, which used to be named Keysun, in the Adıyaman Province of rural southeastern Turkey. The fortress was a stronghold of the crusader County of Edessa. In 1131, the Danishmend Emir Gazi besieged the place. Joscelin I, Count of Edessa, hastened to relieve the defenders and died somewhere in the vicinity.