The Assyrian Rock Relief at Yagmur in the Tur Abdin publishes a newly discovered rock relief in the Mazidagi Plain, at the western end of the Tur Abdin in southeastern Turkey. The preserved remains include an image of an Assyrian king, divine symbols and traces of three panels of cuneiform inscription. Both the image and the panel preserving the most coherent section of legible text can be dated to the time of Tiglath-pileser I. The sequences which can be deciphered relate to the king’s penetration into the northwest undertaken in the course of his third campaign against the Nairi lands. The monument is studied in the context of our understanding of the Assyrian expansion in this sector, together with a review of the settlement pattern and political organisation of the Tur Abdin as presented in Assyrian sources.