Gerger Castle The Gerger Castle is located in Oymakli village in Gerger District of Adiyaman. It was originally built by Arsemes in the 3rd century BCE on the west bank of the Euphrates River. As a border structure of Commagene, the castle served as a lookout for locals crossing the river. It is located on steep rocks and consists of a Lower and Upper Castle. Additionally, it was the first administrative center of the kingdom and also served as a sacred temple. Built with solid walls, the castle is surrounded by steep rocks. On the back of the monument, there is a relief with writing from King Samos, who was the father of Mithridates Callinicus, the King of Commagene. King Samos was also the founder of Somosata, which was also known as Samsat.