Only the original tapered profile of the circular stone base gives the game away: this is a Martello tower, one of twelve built north of Dublin in the early nineteenth century, now divided into four apartments and wedged between a coastal road and the sea.

Martello towers are low, thick-walled circular fortifications, originally developed as coastal defence structures, and the Irish examples were built in response to the real threat of Napoleonic invasion. Construction of the Dublin-area towers commenced in 1804 under the supervision of Colonel Benjamin Fisher of the Royal Engineers, and by December 1805 all were armed and complete. Carrick Hill was designated Tower No. 4 in the northern chain. Each of the twelve northern towers mounted a single 24-pounder cannon, with the exception of the tower on Ireland's Eye, which carried two; unusually, no gun batteries were built to accompany any of them. The Carrickhill tower was staffed in a relatively modest capacity, mainly by an Invalid Gunner of the Royal Artillery, a designation used for soldiers who had been wounded or were otherwise unfit for active field service. The military purpose had run its course by 1874, when the tower was disarmed, and in 1928 it was sold and converted into living accommodation.

The conversion has been substantial. An upper storey and crenellated parapet were added, the bay window appeared on the east side, and a wing was attached to the north; the National Inventory of Architectural Heritage dates a further extension to around 1970. Despite all of this, one original feature survives intact: the machicolation above the western doorway. A machicolation is a projecting gallery or opening in the wall through which defenders could drop stones or other materials on anyone attempting to force an entrance, and its presence here is a quiet reminder of what the building was designed to do. The tower sits directly on Strand Road and is now a private residence, so there is no access to the interior, but the exterior, particularly that western doorway with its projecting stonework, is visible from the road.