Warwick Castle is a medieval castle in Warwick, the county town of Warwickshire, England. It sits on a bend on the River Avon. The castle was built by William the Conqueror in 1068 within or adjacent to the Anglo-Saxon burh of Warwick. It was used as a fortification until the early 17th century, when Sir Fulke Greville converted it to a country house. It was owned by the Greville family, who became earls of Warwick in 1759, until 1978.