Aughinish Martello Tower, Aughboy, Co. Clare

It is an odd shape for a building to survive in, ovoid rather than round or square, its walls battered so they slope inward as they rise, thickest at the base where a cannon shot might have landed. A visitor expecting ruin finds instead something closer to a fortified cottage: glass now sits where a gun platform once did, and a modern chimney rises from what was built as a killing floor.

The tower dates from 1810 to 1811, part of a chain of coastal defences thrown up around Ireland and Britain in response to the threat of French invasion during the Napoleonic Wars. Martello towers took their name and design from a fortification at Mortella Point in Corsica that had impressed British forces with its resistance during an assault in 1794; the type was copied widely, always with the same logic of thick walls, a single elevated entrance, and a flat roof for mounting artillery. This example follows the pattern in cut limestone, three stages of it, with a plinth at the base and square-headed openings that would originally have been narrower, designed for defence rather than daylight. Like many of its kind around the Irish coast, it long outlived the war it was built for, standing empty or serving minor uses until, in 1987, it was sold for conversion to residential use.

That conversion has left its mark plainly on the fabric. The replacement timber casement windows and matchboard door sit within openings that were never meant to be comfortable, and the external metal stair to the entrance recalls, in a domesticated way, the original arrangement whereby a Martello tower's door was set above ground level and reached by a removable ladder, a simple defence against anyone trying to storm the place. The flat roof, once open to the sky and built to bear the recoil of a gun, now carries a cut-limestone parapet and glazing, with cut-stone chimneystacks rising where smoke from a garrison's fire would once have needed careful venting. Seen from the estuary shore, the tower still reads, at a distance, exactly as its builders intended: a blunt, watchful shape against the water, its later domestic life legible only on closer approach.