This iron Age Hillfort is believed to some 2500 years old. It is estimated that about a third of the fort's northern end has suffered from sea errosion. Dinas Dinlle takes its name from one of the Welsh legends of the Mabinogi and the story of Math mab Mathonwy and Lleu Llaw Gyffes, who gave his name to the hillfort Dinlle ('din' in old Welsh meaning fort and 'Lle' short for Lleu).