In the 1550s, County Louth was the rough hem of the Pale - the English-controlled district radiating out from Dublin, the line beyond which Tudor authority frayed and Gaelic Ireland reasserted itself. The Barnewells, an old Anglo-Norman family with deep Louth roots, needed a fortified house that could shrug off a raid. What they built is a textbook example of an Irish tower house: a tall, narrow stone keep with thick walls, a corbelled parapet, and a single defensible entrance. Arrow loops, including a decorative one on the first-floor south elevation, pierce the walls to north, south, and east. Eight kilometres inland from the coast at Annagassan, on fertile arable land, Athclare was a working farm wrapped around a defensive core - prosperous enough to be worth holding, exposed enough to need holding.

The Barnewells kept Athclare into the 17th century. By the 1650s, when the original structure was extended, the castle had passed to the Taaffes - another Old English Catholic family of the region. Then came Cromwell. The Cromwellian conquest of Ireland in the 1650s reshuffled landownership with brutal efficiency, and Athclare was no exception. The Townleys of Lancashire moved in, renting the castle from Erasmus Smith of Edmondthorpe, the businessman and educational philanthropist who had been granted the land. In 1661, Henry Townley is recorded as living at Athclare. His papers, collected by later historians, survive as one of the most useful documents we have of social life in mid-17th-century Louth. The castle changed hands but never went out of use.

By the 1840s the castle was being adapted again. Out-buildings rose around the tower to form a north-facing courtyard. A two-storey house was eventually attached directly to the west wall. The result, today, is one of Ireland's more unusual surviving tower houses: a fortified medieval keep with circular cast-iron downpipes, a steel gate, and uPVC casements where defenders once watched the road. The Record of Monuments and Places number LH018-040 marks Athclare as a national monument under the Guardianship of the Irish state, even though the property itself remains in private hands. The historian Henry G. Tempest, writing in the 1940s, described the castle as it then stood. Two fine stone fireplaces have since been moved into the adjacent dwelling - taken, but not lost.

Tower houses like Athclare were once everywhere in Ireland. The 16th century produced thousands of them, scattered across the country as the principal building type of the Gaelic and Old English gentry. Most are now ruins or rubble, picked over by farmers for stone or simply slumped back into their fields. Athclare endures because it never stopped being useful. The pointed-arch doorway, the dressed limestone voussoirs, the cross loops and angle loops in the upper walls - all are still there, sharp-edged where the weather has not got at them. A red-brick corbelled chimneystack rises from a roof that is now slate rather than thatch. The castle stands complete to the parapet, which is rare. Tempest's mid-century note has aged into a kind of certificate of survival.