Cromwell's Castle, Banagher, Co. Galway

What stands on the riverbank is a squat, rectangular block of rubble limestone, two storeys high, with round turrets clamped onto its south-west and south-east corners and oddly curved, softened corners to the north. That asymmetry of shape, round towers on one diagonal and curved shoulders on the other, is not a design flourish so much as the scar tissue of two different centuries of military thinking layered onto the same walls.

The core of the building dates to around 1650, raised to command the river crossing at Banagher, a point on the Shannon important enough to fortify even in the disordered mid-seventeenth century. It stayed in some form of use long enough to be swept up in a much later wave of anxiety, and around 1805 it was converted into a battery as part of the chain of defences built along the Shannon against the possibility of a Napoleonic landing. Inland gun positions of this kind are unusual in Ireland, where most coastal defence of the period faced the sea rather than a river crossing deep in the midlands, which is part of what makes this stretch of the Shannon's fortifications worth noting. The conversion left its own fingerprints: a camber-arched door on the south side, framed in yellow brick voussoirs, and square-headed windows to the east with yellow brick jambs and limestone sills, all set into the older limestone fabric. Narrower openings elsewhere, barred rather than glazed, hint at the building's later purely military function rather than any domestic one.

The castle sits within a stone-lined moat that wraps around its east, south and west sides, and a battered, sloping base survives at the south-east tower, a defensive device meant to deflect cannon fire and make mining or scaling the wall harder. It is disused now, its dressed limestone parapet and coping still tracing the roofline against the sky, a landscape marker on the river rather than an active structure. Nothing about its later, plainer brickwork undoes the sense that this is a building that answered two different wars a century and a half apart, and wears the evidence of both.