English: Carlisle Castle is over 900 years old. It was first built in 1093, during the reign of William II who ordered the construction of a Norman-style motte and bailey castle on the site of an old Roman fort to protect the northern border of England against the threat of invasion from Scotland. In 1122, Henry I ordered a stone castle to be constructed on the site. Thus a keep and city walls were constructed. The De Irebys Tower dates from the thirteenth century and is a Grade I listed building (Historic England List Entry Number: 1197000 ). Today the castle is managed by English Heritage and is open to the public. Until recently, the castle was the administrative headquarters of the former King's Own Royal Border Regiment now county headquarters to the Duke of Lancaster's Regiment and a museum to the regiment is within the castle walls.