What looks at first like a minor fortification is in fact one of the oldest surviving windmill towers in Ireland, built in 1273 and still legible enough in its fabric to reveal how the machinery once worked.

The tower measures roughly 6.9 metres across on the outside and stands just over six metres tall, with opposing doorways on the east and west faces framed by flat arches supported on timber planks. Inside, the ground floor retains simple window openings and sets of putlogs, the small holes in masonry that once held horizontal timbers, here used to brace the milling machinery rather than scaffolding. The first floor was carried on eight joists built directly into the wall and lit by four windows; the second floor, heavier in construction and windowless, was supported on two large beams. Most telling of all is the wall-head, where sixteen vertical slots arranged in pairs on the inner and outer faces of the stone, and connected by putlogs, almost certainly formed the housing for a rotating cap, the mechanism that allowed the sails to be turned to face the wind. A windmill of this type, a tower mill with a moveable cap rather than a fully rotating body, represents a reasonably sophisticated piece of medieval engineering. The mill is also depicted on the Strafford maps of around 1636, meaning it was still known and recorded as a landmark some three and a half centuries after it was built. The tower sits on a revetted mound nearly eighteen metres across at its base, itself encircled by a fosse, a defensive ditch, and an outer bank, with a stone-lined causeway crossing the fosse to the north-east. Whether the mound is earlier in origin and simply reused, or was raised specifically for the mill, is not settled.

The structure was conserved in 2011 by the St. John's Parish Heritage Group, working with the Heritage Council and Roscommon County Council under conservation architect Kevin Blackwood. The work stabilised the tower without masking the features that make it so readable, including the putlog holes and wall-head slots that tell the story of what once turned above the stone.