The Tanat Valley (Welsh: Dyffryn Tanat) is a large valley in northern Powys, Wales, formed by the course of the River Tanat and its tributaries. Situated south of the Berwyn range, the valley forms from at Llangynog from the merger of two narrow valleys, the Cwm Pennant and Cwm Rhiwarth. Various historic sites, including the Iron Age hillfort Llwyn Bryn-Dinas and the medieval St Melangell's Church are located along the valley. Largely agrarian, sheep farming has formed a major industry in the region for several centuries. Large-scale slate and lead mining in the region lasted from the 16th to late 20th century, although earlier mines possibly existed during the Iron Age.