But on high ground to the north-west, a rectangular earthen mound sits quietly, its identity still not entirely settled. It measures roughly 30 metres north to south and 23 metres east to west at the base, narrowing to a flatter platform on top, and for a long time it was read as a motte, the raised earthwork at the centre of a motte-and-bailey castle, a Norman form of fortification in which a timber or stone stronghold occupied an artificial mound beside an enclosed courtyard or bailey. T. J. Westropp, writing in 1915, recorded a surrounding fosse and an outer mound consistent with that arrangement. Landscaping has since removed the fosse, but the slightly raised sub-rectangular lawn to the south of the mound, sitting one to three metres above the surrounding ground, may correspond to what Westropp identified as the bailey.

When John Hunt partially excavated the mound in 1959, he came away with a different reading. Rather than an early medieval Norman fortification, he concluded it was a gun emplacement, probably constructed during the seventeenth-century conflict between Royalist defenders and Confederate Irish forces who eventually took the castle. Admiral Penn, in his account of the castle's defence, mentions four cannon, and Hunt argued this mound was the position from which they were deployed, commanding what was then a broad channel of water separating the castle from the higher ground to the north. He suggested that gabions, essentially wicker baskets packed with earth, or a fence of stout logs would have lined the top of the mound to protect the guns and their crews from incoming fire. Burned material found in the fosse during excavation supported his theory: he proposed it represented the remains of that defensive barrier, set alight after the castle fell to the Confederates. Hunt also uncovered the lower courses of what may have been a sixteenth-century house beside the mound, adding another layer to an already complicated site. Where the original Anglo-Norman motte actually stood remains unresolved; an alternative location west of the Castle Hotel and church, across the road, has been proposed as a more geographically plausible position for such a structure.