The Romans, the first to realize Cardiff's strategic position on the River Taff near the Bristol Channel, built a series of forts on this site, controlling the whole of Wales by 75 AD. From around 250 AD until the 5th century, Cardiff gained importance as a naval base for the protection of the Roman Empire.

Robert Fitzhamon, the Norman Lord of Gloucester, who had been drawn into the feuds among the Welsh Princes, saw the strategic importance of the old Roman fort at Cardiff and built a Norman castle on the site with a forty-foot motte (defensive hill), moat and timber Keep. In the 12th century his son-in-law, Robert "the Consul," is credited with building the first stone keep of Cardiff Castle...