Lancaster (lăngˈkəstər) [key], city (1991 pop. 43,902) and district, county seat of Lancashire, NW England, on the Lune River. The city's products include furniture, textiles, synthetic fiber, farm machinery, linoleum, and soap. It also has an active livestock market. Lancaster Castle occupies the site of a Roman station. The castle has a Norman keep and tower (built 1170) with a turret called John o' Gaunt's Chair. St. Mary's Church dates from the 15th cent. Lancaster has a university and a civic and regimental museum.