It began as the seat of power of the Norman, then Angevin rulers before falling out of favour as a royal stronghold during the 12th and 13th centuries. It was still valued however, possibly because of its position on the road between Portsmouth on the southern coast - England's main port for trade with southern France and the Iberian Peninsula - and London - valued enough for the young Henry III to build a "Great Hall" for royal occasions within the castle's grounds.
The hall, construction of which was started in 1222, is the only part of the fortress still viable. The castle itself found itself on the wrong side during the English Civil War and was demolished by Cromwell.
These days it is a popular tourist attraction. In the late Middle Ages Winchester was linked by Sir Thomas Malory and others with the legend of Camelot and the Round Table and other things Arthurian. A late 13th century "replica" of the Round Table (complete with Tudor Rose at the centre after a refurbishment during the reign of Henry VIII) hangs from a wall.