The transformation is striking, but the original structure beneath the domestic additions is largely intact: thick, battered granite walls, the term referring to walls that slope slightly inward as they rise, built to deflect cannon fire, and small defensive openings that leave little doubt about the building's origins. Constructed between 1804 and 1805 as part of a coastal defensive chain, the tower is one of a series of Martello towers, squat circular fortifications developed in response to the threat of Napoleonic invasion, that were erected along the Irish and British coastlines in the early nineteenth century.

This particular tower, designated No. 2 in the local sequence, was paired with a four-gun battery on its seaward side. Three of those guns were positioned to fire northwards and eastwards across Killiney Bay, covering the open water approach. The fourth faced south along the beach toward a neighbouring tower and out to sea, meaning the battery could engage threats from almost every direction. Its specific strategic purpose was to protect the estuary of the Dargle River, a stretch of coast that, as Paul Kerrigan noted in his 1995 study of Irish fortifications, had no harbour at the time the tower was built. Taylor's map of the Dublin environs, surveyed in 1816, records both the tower and the battery, offering a rare early snapshot of the complex before the coastline around it changed significantly over the following century.