This is a columbarium, a dovecote, built to house pigeons as a reliable source of meat and eggs for the religious community next door. What makes it unusual is not just its survival, but the sheer precision of its construction: eleven tiers of nesting boxes, thirty-two to each circuit, each box roughly 22 centimetres wide and 20 centimetres high, rising to a height of around five metres. Above that, the wall curves gradually inward before being corbelled steeply to leave a circular opening at the top, a design that would have allowed birds to fly in and out while keeping the interior relatively sheltered.

The priory at Ballybeg was an Augustinian foundation, and it is almost certainly the canons there who commissioned this structure as part of the working infrastructure of their community. The columbarium is entered through a ground-floor door on the west side, but there is a second, more intriguing entrance higher up on the north face, a lintelled door set well above ground level that opens onto mural stairs leading to the top of the tower. Projecting masonry to the east of that upper door suggests that a wall once extended northward from the columbarium, likely carrying a wall-walk from which the upper door could be reached at floor level. The antiquary R. R. Brash recorded plans and sections of the building in 1852, and his drawings remain a useful reference for understanding the structure's geometry. The internal diameter of the tower is 4.6 metres, modest enough that the density of nesting boxes on every surface would have made the interior feel almost entirely alive with pigeons when in use.