Rhuddlan may not be as well known as some of the North Wales castles, yet it shares much in common with its illustrioius neighbours. Like Caernarfon and Conwy, it was built as one of the 'iron ring' of fortresses by the English monarch Edward I, in his late 13th-century campaigns against the Welsh. Its massive twin-towered west gatehouse - heralding the inner core of a characteristic concentric 'walls within walls' system of defences - immediately catches the eye. But possibly the most impressive engineering achievement here is the way in which access for ships to the castle from the sea - almost 3 miles away - was made by canalizing the River Clwyd, a mammoth task involving 1,800 ditchers. Remains of a defended river gate can still be seen in the outer ring of walls, overlooked by the towers of the powerful-shaped inner ward.