The reason for that small kink in the tarmac is a ringfort, an ancient earthwork enclosure that was already old enough to command respect when the road was laid out. The road-builders curved around it rather than cut through it, though the eastern side of the monument suffered some damage in that process all the same.

A ringfort, or rath, is an enclosed settlement typical of early medieval Ireland, usually circular and defined by one or more earthen banks and an external ditch. This example at Ballycannan is subcircular in plan, measuring roughly 50 metres north-northwest to south-southeast and 45 metres in the perpendicular direction. Its defining bank and fosse, the fosse being the ditch dug to provide material for the bank, are still present, though unevenly so. The northern section of the bank is the best preserved, standing between 2.5 and 3 metres high and 3.5 metres wide; the fosse survives only along the southwestern arc, where it remains about 3 metres wide and half a metre deep. Two gaps interrupt the circuit, a wider one of roughly 6 metres at the north that may represent the original entrance, and a narrower 3-metre opening at the south. By 1980, when Ryan recorded the site, heavy vegetation covered both the interior and exterior, and that growth has done little to make the earthworks any easier to read. The site is protected by a preservation order under the National Monuments Acts, which is partly why the road swings wide of it rather than simply erasing it.