St John the Baptist's Church is the Church of England parish church of the village of Clayton in the district of Mid Sussex, one of seven local government districts in the English county of West Sussex. The small and simple Anglo-Saxon building is distinguished by its "remarkable" and extensive set of wall paintings, dating from the early 12th century and rediscovered more than 700 years later. Much of the structural work of the church is 11th-century and has had little alteration. The church, which stands in the middle of a large churchyard and serves the hamlet of Clayton at the foot of the South Downs, is part of a joint parish with the neighbouring village of Keymer—an arrangement which has existed informally for centuries and which was legally recognised in the 20th century. English H