In October 2021 the presence of ancient remains on a ridge below the 2000m summit of Kımıl Dağı in the Gerger district of Adıyaman province was reported to Adıyaman Museum. Investigations by archaeologists from the Museum revealed the existence of a previously unreported sanctuary belonging to the ruler cult of Antiochus I of Commagene. Two substantial limestone stelai recovered from the site have now been brought to the Perrhe Archaeological Park. One of the stelai carries a relief showing Antiochus shaking hands with a divine figure seated on a mountain peak. A long inscription recording the establishment of the sanctuary and a sacred law regulating its associated cult begins on the reverse face of the relief stele and continues onto a separate block and both faces of a second stele. In this article we provide a first publication and analysis of the inscription, and in the light of the information provided by it reconsider the significance of the relief. The novel features presented by the relief and the inscription raise new questions about the development of Antiochus’ ruler cult and the weight of local religious tradition in shaping its form which are explored in the concluding sections of the article.