Sion (syôN) [key], Ger. Sitten, town (1993 pop. 25,300), capital of Valais canton, SW Switzerland, on the Rhône River. An ancient town, Sion is now a wine and horticultural market center. There are hydroelectric plants and coal mines nearby. Sion has been an episcopal see since the 6th cent. The town is rich in historic remains, among which are a 13th-century castle, a late Gothic cathedral, and a 17th-century town hall.