Rhuddlan was planned as a concentric castle. It has a unique 'diamond' in layout as the gatehouses are positioned at the corners of the square baileys instead of along the sides like at Flint, Harlech or Beaumaris. The inner ward has defensive walls with twin-tower gatehouses. The outer ward is surrounded by a curtain wall that has small towers and turrets. The castle also had a dry moat to improve defence on its landward side. Within the inner ward there was a great hall, kitchens, private apartments and a chapel. The outer bailey had a granary, stables and a smithy. Much of the work was overseen by master mason James of St George. Rhuddlan, which was not completed until 1282, was built concurrently with Flint Castle. Rhuddlan is next to the River Clwyd. During the fortification's lengthy construction, the river course was straightened and dredged to allow ships to sail inland along a man-made channel. Its purpose was to allow provisions and troops to reach the castle even if hostile forces or a siege prevented overland travel.