Ballmacotter Castle, Ballymacotter, Co. Cork

Most of the signal towers built along this stretch of coast have long since lost their hanging slate to weather and neglect, leaving bare stone or rendered walls where a protective skin once kept out the rain. This one has kept its covering largely intact, even as the building itself has been reworked to serve a domestic purpose far removed from its original brief.

The tower dates to 1804, part of a chain constructed around the Irish coastline during the Napoleonic wars, when British authorities anticipated a French invasion and needed a way to pass warnings rapidly from headland to headland. The plan was straightforward in theory: a line of towers, each within sight of the next, relaying signals along the coast faster than any horse or ship could carry a message. In practice, the scheme ran into a problem nobody in London had accounted for, the wet, mist-laden climate typical of Ireland's west coast, which frequently swallowed the visual signals before they could be read. A network built for speed and certainty ended up hostage to fog.

What survives is a square-plan tower of two bays and two stages, originally built as a freestanding structure but now absorbed, in part, into use as a house. Its projecting bartizans, the small overhanging turrets at the corners that would once have allowed defenders to watch the approaches below without exposing themselves, are finished in red brick and render, while the main roofline carries limestone copings. The square-headed window openings show the marks of adaptation over two centuries, some blocked up entirely, others fitted with modern uPVC replacements. None of this softens the slate hanging, though, which remains the tower's most telling feature, a rare surviving example of the material that once wrapped most of these structures before time and weather stripped it from its neighbours.