Guarding the ancient ford of the river Clwyd a flashpoint of Anglo-Welsh border warfare since the days of the Saxon King Offa, Rhuddlan was the strongest of Edward I's castles in north-east Wales.

Begun in 1277, it was linked to the sea by an astonishing feat of medieval engineering, a deep-water channel nearly 3 miles (5km) long. Some seventy "dikers" worked continously for three years to divert and canalise the river, allowing Edward's ships to sail right up to the castle.

Designed by the famous architect James of St George, the castel was the first of Edward's revolutionary "concentric" fortresses, the precursor of Conwy, Harlech and Beaumaris. Its core is a perfectly symmetrical diamond-plan stronghold, equipped with two corner towers and twin gatehouses. Beyond was an outer circuit of turretted walls, and beyond again a moat linked to the new canal.

The king's forward base for this conquest of north Wales, Rhuddland was also a favourite with his Queen Eleanor; some believed it was here that their son was declared the first English Prince of Wales. Though shattered by time and deliberate destruction following a Civil War siege, Rhuddlan still proclaims the innovative genius of its architect, and the achievement of the unsunglabourers who toiled for just over a penny a day.