Post medieval earthwork. The mounds at the centre of Peel Castle almost certainly represent a modernisation of the castle's defences during the Civil War. The 7th Earl of Derby pent considerable resources fortifying the Isle of Man between 1643-1651, and the earthworks form a somewhat irregular 'star fort' or sconce designed to protect artillery from cannon-fire. At the centre of the earthworks lies the Dyal Mound, its sides orientated towards the four cardinal points of the compass. Its name reflects the presence of two sundials recorded on its summit during the 18th century.