Malin Signal Tower, Ardmalin, Co. Donegal

Machicolations, projecting stonework at parapet level once used for dropping objects on attackers below, survive at two corners and along the north elevation, giving the structure a faintly military bearing that has little to do with its later, quieter working life. The cement render applied around 1900 has weathered unevenly over the rubble stone beneath, and the pronounced batter, or outward slope, at the base of the walls is one of the few details that still hints at its original defensive purpose.

That purpose dates to the early 1800s, when Britain, rattled by a French landing at Killala in County Mayo in 1798, ordered the construction of over eighty signal towers around the Irish coast between 1804 and 1806. Built to a broadly standard design, they relied on a system of flags and balls run up a mast on the seaward side, each tower passing warnings of enemy ships along the chain to its neighbours. Height and a clear line of sight mattered more than comfort, which is why these buildings so often occupy the most exposed ground available; this one was largely complete by 1804, with a signal lieutenant appointed in February 1806. The urgency did not last. Nelson's victory at Trafalgar in 1805 removed the immediate threat of invasion, and by 1809 the network was stood down. The tower's working life, though, was far from over. By the 1870s it had become a weather station, and around 1890 it was pressed into service again as a signal station for Lloyds of London, relaying news of transatlantic shipping arrivals via a semaphore link to the offshore island of Inishtrahull before the information travelled on to London. In 1901 Guglielmo Marconi set up a radio station beside the tower, and in 1902 sent the first commercial radio message from Malin Head to the ship SS Lake Ontario; the station later took part in trials connected with the radio equipment aboard RMS Titanic in 1912, before eventually passing into the hands of the Post Office as a telegraph station.

Little of the original fabric remains intact today. The doorway on the north side, probably the original entrance, is blocked with modern blockwork, as are most of the window openings, and the flat roof behind the raised parapet has fallen in entirely. Traces of single-storey additions once attached to the east and west walls have been demolished, leaving only scars on the stonework. Nearby stand the remains of a World War Two watchman's hut and the probable footprint of the earlier telegraph and semaphore station, so that the tower now forms part of a small cluster of structures spanning more than a century of coastal watching, from Napoleonic-era alarm to wartime lookout to the first stammering messages of wireless radio.