The castle is located in the Oymaklı Village of the Gerger District of Adıyaman. The Gerger Castle (Gerger Kalesi) is located on the west bank of the Euphrates River and was founded by Arsemes in the 3rd century BCE. The castle forms the eastern border of the Commagene Kingdom and is the control point of the crossroads over the Euphrates River (Fırat Nehri). The Gerger Castle was built on steep rocks and consists of a Lower Castle and Upper Castle. It was the first administrative centre of the Kingdom of Commagene, which at the same time served as a sacred temple.

The castle is located on a steep rock and surrounded by solid walls. On a large rock surface, there is a gigantic relief and inscriptions of King Samos (140-100 BCE), the father of the King of Commagene Mithridates Callinicus and the founder of Somosata (Samsat), which was the capital of the Ancient Commagene Kingdom.