Thornbury Castle is a Tudor castle in the parish of Thornbury, in Gloucestershire, England, situated next to the parish church of St Mary, founded in the Norman era. Construction was begun in 1511 as a further residence for Edward Stafford, 3rd Duke of Buckingham, of Stafford Castle in Staffordshire. It is not a true military fortress but rather an early example of a Tudor country house, with minimal defensive attributes. It is now a grade I listed building.