Lancaster Castle is a medieval castle in Lancaster in the English county of Lancashire. Its early history is unclear, but may have been founded in the 11th century on the site of a Roman fort overlooking a crossing of the River Lune. In 1164, the Honour of Lancaster, including the castle, came under royal control. In 1322 and 1389 the Scots invaded England, progressing as far as Lancaster and damaging the castle. It was not to see military action again until the English Civil War. The castle was first used as a prison in 1196 although this aspect became more important during the English Civil War. The castle buildings are owned by the British sovereign as Duke of Lancaster, which leases part of the structure to Lancashire County Council who operate a Crown Court in part of the building.
Until 2011, the majority of the buildings were leased to the Ministry of Justice as Her Majesty's Prison Lancaster. The Castle was returned to the Duchy's ownership by the Ministry of Justice in 2011. The Castle is now open to the public seven days a week and is undergoing a large-scale refurbishment to allow access to more areas.