What makes Carrowmably stranger still is the ground it occupies. The tower sits within a large circular enclosure that is thought to date to the Neolithic period, its external ditch and internal bank still legible in the surrounding pasture. Inside that older earthwork, a smaller sub-circular ditched enclosure is suspected to be early medieval in origin. A mortared stone wall cuts east to west across the whole arrangement, partitioning off the tower and the northern third of the enclosure from the rest. The result is a building from the early 1800s embedded in a landscape carrying perhaps five thousand years of accumulated use, each phase largely indifferent to the one before it.

The tower was built between roughly 1804 and 1806 as part of a network of over eighty signal stations commissioned by the British Board of Ordnance in response to the threat of a French invasion fleet. The chain ran clockwise from Dublin Bay all the way around the Irish coast to Malin Head in County Donegal, with signalling between stations carried out using a naval signal post. The Carrownrush tower is among the better-preserved examples: its parapet survives on all sides, complete with chamfered cut stone coping, and bartizans, small projecting corner turrets supported on sloping corbels, protect the south-east and south-west corners, each fitted with narrow gun loops. A machicolation, an overhanging defensive projection above the north wall doorway, guards the original first-floor entrance, which would have been reached by a retractable ladder. Internally, joist-holes in the walls trace where wooden floors once sat, and a square drainage channel in the south-east corner is thought to have carried rainwater from the roof down to storage barrels in the semi-basement. The smooth lime render still coats the interior walls. The wooden floors and roof are long gone, but the stone shell has held its shape with unusual completeness. The nearest surviving counterpart in the chain, the Rathlee Signal Tower about ten and a half kilometres to the west-north-west, is currently obscured by forestry; the next link to the north-east, on Knocklane Hill, has largely collapsed. When the threat of French invasion faded in the mid-1810s, the entire system was abandoned.