This impressive motte, standing between 8.5 and 10 metres high with a diameter of roughly 43 metres, forms the centrepiece of what was once a substantial Norman fortification. The main mound is encircled by an external bank, whilst a small D-shaped bailey adjoins the northwestern side, defined by its own earthen rampart. Though a much larger eastern bailey once existed, appearing as a sub-rectangular enclosure in eighteenth-century illustrations by Wright, modern waterworks have sadly obliterated most traces of this feature, leaving only a faint scarp to mark its original boundaries.

The summit of the motte tells its own peculiar story through the ruins of a late eighteenth-century castellated house known locally as ‘Byrne’s Folly’. This whimsical structure, along with a peripheral bank that appears to date from the same period, represents an attempt to romanticise the ancient earthwork during the Gothic Revival. The folly takes its name from its builder, though it seems Byrne’s architectural ambitions may have exceeded practical considerations, as the structure now stands in ruins. A wide gap in the eastern bank, complete with a causeway across the fosse, provides access to the summit, though whether this entrance is original to the Norman period or a later modification remains uncertain.

Adding to the site’s archaeological complexity, a souterrain has been discovered set into the southern side of the motte, suggesting the location may have had significance in the pre-Norman period. Now designated as National Monument No. 388 under state guardianship, Dun Dealgan offers visitors a chance to explore layers of Irish history, from possible early medieval origins through Norman conquest to Georgian romanticism, all condensed into this remarkable earthwork complex.