Roughly three metres high and about thirty-six metres across at its longest, it was shaped, or at least adapted, into an artillery platform during the seventeenth century, its flat lozenge-shaped summit apparently designed to bear the weight and recoil of cannon. A wide flat-bottomed fosse, the term for a defensive ditch, encircles much of the base, with traces of an outer bank surviving along the southern side. The mound itself is probably largely natural in origin, the kind of glacial feature common enough in the Irish midlands and west, but someone saw in it a ready-made elevated position and put it to work.

The target was the castle that still stands approximately 250 metres to the east. When the mound was in use, this ground looked quite different: it sat close to the shore of an arm of Lough Rusheens, a lake that has since been drained, placing the battery directly opposite the castle across the water. According to records compiled by the Ordnance Survey in the nineteenth century and later published by O'Flanagan, a Captain Elleen transported cannon from Galway and raised this battery specifically to fire on the castle. The account, brief as it is, has the feel of a siege operation conducted with some deliberation, the cannon hauled across the county, a position chosen and prepared, and then the bombardment of a structure that was presumably still occupied and defended. The castle survived, at least structurally, and still stands today.

The mound is situated in open pasture and was recorded on the third edition of the Ordnance Survey six-inch map in 1930 as an oblong mound. On the ground it reads as an oval hillock with a slight hollow at the centre of its summit, that depression possibly the lasting trace of where the guns once sat.