Ruthin is a market town and community in Denbighshire, Wales, in the south of the Vale of Clwyd. It is the county town of Denbighshire. The town, castle and St Peter's Square lie on a hill. Ruthin is skirted by villages such as Pwllglas and Rhewl. The name comes from the Welsh rhudd and din, after the colour of the sandstone bedrock of which the castle was built in 1277–1284. The original name was Castell Coch yng Ngwern-fôr. The Old Mill, Ruthin, is nearby. Maen Huail, a registered ancient monument attributed to the brother of Gildas and King Arthur, stands in St Peter's Square.