The builders of this medieval fortification transformed the existing hill into a formidable defensive structure, scarping its sides to create a steep, flat-topped mound measuring 19.2 metres across from north to south and rising 11 metres high. What makes Tullahedy particularly unusual is the berm, a metre-wide ledge that runs around the hillside halfway up, which expands on the southern side to form an elevated bailey; a rare defensive arrangement in Irish castle construction.

The motte’s defences are impressively comprehensive. At its base, a wide fosse or defensive ditch, measuring between 4 and 6 metres across and up to 2.5 metres deep, encircles the entire structure with its distinctive flat bottom. Beyond this lies an external bank constructed from earth and stone, 4 metres wide and originally standing a metre high, though the northern sections from the northwest through to the northeast have been significantly reduced over time. A stone-lined causeway, 2 metres wide, cuts through these defences on the southern side, likely providing the original access route to the elevated bailey.

Today, field clearance stones have been piled against the northern base of the mound, a practical reminder of the site’s long history as part of the working landscape. The castle represents a significant example of Anglo-Norman fortification in Ireland, with its unusual defensive features suggesting either adaptation to local conditions or perhaps the work of builders experimenting with different defensive strategies. The site was documented in ‘The Archaeological Inventory of County Tipperary, Volume 1’ by Jean Farrelly and Caimin O’Brien in 2002, with subsequent research adding to our understanding of this remarkable medieval structure.