Read a comprehensive and useful History of Cardiff Castle
See the above link for the useful history of Cardiff Castle. Some people do not realise it is a genuine medieval castle, because of the considerable alterations by the Bute Family. The ornate clocktower and other Victorian improvements are quite separate from the Castle's tower, or Great Keep, resting on the raised ground in this picture.
The castle goes back to Roman times, as there were Roman Barracks and a fort on the land now occupied by the castle.