York castle began as a motte and bailey castle built on the orders of William the Conqueror in 1068, one of many such castles built across the land to help William solidify his power. However the castle was destroyed the following year by the Vikings. The castle was rebuilt on a much greater scale and included a moat.
Henry III rebuilt the castle in stone in the mid thirteenth century. The current keep, also known as the Clifford Tower (shown below), dates from this construction. York castle became one of the most important centres of royal power in the North.
However by the time of Elizabeth I the castle has fallen into disrepair and was no longer considered an important military strongpoint. The castle was used as a prison and centre of administration. The prison continued to be used (though with some later rebuilding) until 1929. Part of the castle is still used as a crown court, it also includes a museum.