Lincoln Castle is a major castle constructed in Lincoln, England during the late 11th century by William the Conqueror on the site of a pre-existing Roman fortress. The castle is unusual in that it has two mottes. It is only one of two such castles in the country, the other being at Lewes in Sussex. Lincoln Castle remained in use as a prison and law court into modern times, and is one of the better preserved castles in England; the Crown Courts continue to this day. It is open to the public as a museum. Lincoln castle remains one of the most impressive Norman castles in the United Kingdom.