Nottingham Castle is an earthwork motte and bailey fortress, founded in 1067 by William the Conqueror. In 1170, King Henry II, founded the stone castle, when making the site the principal royal fortress in the Midlands. The only surviving medieval remains of the upper bailey is Mortimer's Hole, a passage which leads to the base of the rock. In the middle bailey are the foundations of the Black Tower, King Richard's Tower and traces of the bailey curtain wall and ditch. The very large outer bailey retains part of its resorted curtain wall, with two round flanking towers and a huge twin-towered gatehouse. After the Civil War, the castle was slighted and then all the standing remains were destroyed in the building of a 17th century ducal mansion. 7 miles north-west is Greasley Castle and 12 miles east is Aslockton Castle.