lewelyn ap Gruffyfdd the Prince of Wales had consistently failed to do homage to Edward I, King of England. The Welsh Prince had been paying sums of money to the English crown as agreed in the Treaty of Shrewsbury of 1267, but after the death of Henry III the payments had stopped. Edward's repeated demands for a meeting with Llewelyn were ignored and in an attempt to stir up internal problems in England, Llewelyn had sent to France for Eleanor de Montfort who had been promised to him as a bride for his involvement in the Baronial revolt against Henry III. Eleanor was captured by the English on the journey to Wales and was kept prisoner by Edward. Edward had no choice but to deal with the rebellious Llewelyn and began his war on the Welsh with a massive programme of castle building.

o successfully attack the Welsh in the north of the country, Edward had to have a strong supply line for his army. Invaders of Wales had always found it hard to subdue the Welsh because it was easy for the Welsh to use the mountainous terrain to cut off attacking armies from their supplies. To solve the problem Edward built a series of castles along the north coast where they could be easily resupplied from the sea. Flint Castle in Clwyd was begun in 1277 and was one of the first castles to be started. Rhuddlan Castle was started shortly afterwards. The design of these castles was based on fortifications Edward had had seen on his travels in France and consisted of a strong castle attached to an enclosed town. The town was populated with English traders who could supply the army and start trading with the local Welsh people.