Balbriggan Martello Tower, Bath Road, Balbriggan, Co. Dublin

The parapet that once ran round the summit is gone entirely, leaving only the corbelled brackets that supported its platform jutting into open air, small stone ledges holding up nothing. It gives the building a slightly unfinished look, as though the masons simply stopped, though what actually happened is erosion of purpose rather than construction: the upper defences were never meant to last this long unaltered.

The tower dates from around 1805, part of the chain of coastal defences thrown up along the Irish and British coastlines during the Napoleonic invasion scare, when the threat of a French landing seemed real enough to justify a string of near-identical stone towers from Cork to Dublin Bay and beyond. Their circular plan and battered, tapering walls were designed for exactly this kind of longevity, deflecting cannon fire that never came, and Balbriggan's example follows the standard pattern in coursed limestone, with patches of the original roughcast render still clinging to the surface here and there. The small window openings are square headed with plain stone lintels, unfussy and functional, built for a garrison rather than a view. At ground level the original door opening has been blocked up, a small but telling alteration that marks the tower's shift from active military use into something more ambiguous, no longer garrisoned, not quite ruined.

What survives is really the lower two thirds of a design that depended on its roofline for both defence and drama; the corbels alone hint at how the platform would have projected outward, giving defenders an overhang from which to fire straight down on anyone attempting to scale the walls. Without that platform, the tower loses the top-heavy silhouette so recognisable elsewhere along this coast, and instead sits closer to the ground, its proportions slightly stubbier than the postcard version of a Martello tower. It rewards a slow look rather than a passing one, the kind of building where the interesting details, the surviving render, the corbel brackets, the sealed doorway, only become legible once you stop expecting a tower and start reading it as a sequence of alterations.