The first castle was built by William the Conqueror's son, Robert Curthose, in the late 11C. The keep is all that remains of the castle he inherited in the 12C. From the top of this huge building you can take in the whole city, the river and the countryside in the distance. In 1848, the decision was made to take the railway line linking up with the main station through the castle grounds, its many archways thus cutting off the keep from the picturesque Black Gate.