New high-precision Ar-Ar dating of basalt underlying the city of Diyarbakir, southeast Turkey, constrains the Quaternary incision history of the River Tigris, strengthening the pre-existing chronology based on magnetostratigraphy and K-Ar dates. The basalt, which overlies Tigris terrace gravel 70 m above the river, is part of the Karacadag shield volcano complex centred ca. 60 km to the southwest. The reverse-magnetised Diyarbakir basalt, one of relatively few flow units to reach the Tigris valley axis, has been dated to 1196 +/- 19 ka (+/- 2 sigma). Two lower terraces have been recognised in the Diyarbakir area, 46 and 32 m above the present river, with at least one other further downstrearn. From this evidence the rate of Middle-Late Pleistocene incision by the Tigris can be estimated; it probably reached ca. 0.07 mm a(-1), reflecting the characteristic global increase in uplift rates observed at that time. Copyright (C) 2007 John Wiley & Sons, Ltd.