mountainous traditional region covering approximately 450 square miles (1,165 square km) in northern Perth and Kinross council area, historic county of Perthshire, Scotland. Enclosed by several ranges of the Grampians, which exceed 3,000 feet (900 metres) in elevation, the Atholl basin, with an elevation of 1,500 feet (457 metres), is entered by the passes of Drumochter in the north and Killiecrankie in the south. Glen Garry and Glen Tilt are the principal valleys, and the chief lakes are Loch Rannoch and Loch Tummel, which is the site of several hydroelectric power stations. Pasture and cultivation centre on the lower valleys. The population is concentrated mainly in Blair Atholl and Pitlochry. Blair Atholl, on the River Garry, is the site of Blair Castle (built 1269), the ancient seat of the dukes of Atholl.