Lancaster Castle and its distinguished neighbor, the priory church, crown the summit of a hill overlooking the River Lune. A Roman fort occupied the site. Following the arrival of the Normans, Lancaster became part of the vast estate granted to Roger de Poitou and the first castle is very likely to have been his foundation.
In 1265, the castle became the chief seat of the powerful lords who followed, including Thomas, ring leader of the baronial opposition to Edward II; Henry, the first palatine duke; and john of Gaunt, who married his way into the duchy. After John of Gaunt's son seized the throne as Henry IV in 1399, and the consequent union of the Duchy of Lancaster with the Crown, the castle fell into decline as a residence but remained the administrative center of the Duchy. It remains very much a working vastle, still serving as a courthouse and prison.
The existing castle is largely a reconstruction of 1788-1823 by Thomas Harrison, designed to meet the growing requirements of the country gaol and the courts. The phony curtain and towers enclose an area roughly corresponding with the medieval bailey, except on the north side where the prison juts out in a big arc. Furthermore, a series of assize buildings, notably the semi-circular Shire Hall, projects on the west.
Fortunately, a few important pieces of the medieval castle have been preserved. The finest of these is John of Gaunt's Gate, one of the most majestic of medieval English gatehouses. It is a massive and rather austere-looking block as befits the entrance to a prison.
There is a continuous machicolated parapet around the wall head and the well-proportioned gateway preserves its original portcullis. Semi-octagonal towers that carry inner turrets above parapet level flank it. The circular Hadrian Tower forms part of the Shire Hall complex.