Lewes (lōˈĭs,–ĭz) [key], town (1991 pop. 14,499) and district, East Sussex, SE England. The county seat of East Sussex, Lewes is a farm market with light manufactures. St. Pancras priory was founded in the town in the 11th cent.; its ruins remain. In 1264, Lewes was the scene of a victory by Simon de Montfort, earl of Leicester, over Henry III.