Greencastle Fort, Battery Brae, Greencastle, Co. Donegal

Below it, a lower courtyard holds the remains of a battery, flanked by walls pierced with gun loops, and at its centre a sunken magazine sits under an earthen mound, built that way so that a direct hit from artillery would be smothered rather than detonating the stores inside. It is an odd, layered piece of military architecture, part fortress and part earthwork, that has since been a barracks, a hotel and visitor centre, and is now simply disused.

The fort belongs to the wave of coastal defences thrown up around Lough Swilly and Lough Foyle after 1798, when a French fleet carrying some 8,000 troops attempted a landing in Lough Swilly and was turned back at sea. The scare prompted a formal review of Ireland's coastal defences under the Gother Mann committee from 1804, and in 1810 a Captain Sir William Smith identified five sites for permanent batteries, at Greencastle, Muckamish, Knockalla, Rathmullan, and Ned's Point near Buncrana. Greencastle was chosen because it commanded the entrance to Lough Foyle and the approach to Derry, a strategic value already recognised centuries earlier by the builders of the adjacent fourteenth century Northburg Castle, now a ruin just to the south-west. Construction began around 1811, but the main contractor, Edward Farrell, had underbid the job badly, tendering about £6,000 for work estimated at £11,000, and the project stalled; when Sir Walter Scott visited in 1814 the guns still were not in place. By the time the fort was finished around 1816, with five 24-pounders on the battery and two howitzers mounted on the tower, Napoleon had already been defeated at Waterloo and the invasion threat it was built against had passed. It was never garrisoned anywhere near its intended strength of three officers and fifty-four men, though it was re-armed in 1860 with a 10-inch gun and 68-pounders following a fresh defence review, and continued to hold a small detachment until the gunners finally left in 1890.

The keystone over the blocked carriage-arch at the south-west entrance is dated 1812, a small, legible fragment of the building's difficult early construction. The barracks buildings ranged around the upper courtyard, the stair tower linking the two levels, and the glacis, a gently sloping bank designed to expose attackers to defensive fire while shielding the walls behind it, to the north are all still traceable in the fabric, even stripped of their original military use.