The motte, erected over a rocky hillock, was some 40 feet tall, and would have been protected by a timber palisade.
During the 12th century, the castle's lord, Robert "the Consul" (the natural son of King Henry I), realized the defensive value of reinforcing his fortress with stone and ordered the construction of the shell keep. The 12-sided keep survives in fine condition, the only significant additions being its 15th century gatehouse and the stairway breaching the sloping motte.
For a time, the keep was the prison of Robert, 2nd Duke of Normandy (and also FitzRoy's uncle), on the command of FitzRoy's father, the king.
Much of Cardiff Castle's history revolves around conflicts with the native populace. In 1183-84 the Welsh revolted, and caused much damage to the castle and its associated town. Even though the powerful de Clare family took hold of the castle (as well as numerous other estates) in the following century, problems persisted with Welsh insurgency.
In the 1270's, when Wales was unified under the leadership of the charismatic Welshman, Llywelyn ap Gruffydd (the Last), Gilbert de Clare refortified the castle in anticipation of further Welsh rebellion. The curtain wall was strengthened and construction of the Black Tower and south gateway was initiated. The much awaited assault never occurred and de Clare's work remains to this day.
Bute despised the result and engaged the architect William Burges, who shared Bute's interest in medieval Gothic Revivalism, to undertake rebuilding.
This shared passion, combined with Bute's almost limitless financial resources, led to Burges re-building on the grandest scale.
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.