Rhuddlan derives its name from the Welsh Rhudd and Glan, which translates as Red Bank. It has a significant place in Welsh history as it was where King Edward I proclaimed the Statute of Rhuddlan, which established a system of government that lasted until King Henry VIII’s Act of Union in 1536. It is also where the English king declared that he would appoint ‘a prince who was born in Wales, could speak no English, and whose life and conversation nobody could stain’, before naming his own son Prince of Wales, in 1301.

The town's most prominent feature is the castle built on the orders of Edward I, between 1277 and 1282. Designed by the master mason James of St. George it was the first fortress in Wales to have a concentric layout with layered defences. It features a diamond-shaped inner ward, flanked by two gatehouses, with a curtain wall and dry moat. As the king liked his castles to be easily supplied and reinforced by sea in case of land siege, the adjacent River Clwyd was dug out by hand and diverted to allow ships to sail right up to the walls.

The castle remained in use until 1647 when it was slighted by Cromwell's Parliamentary forces to prevent it being used for further military purposes.