Drumlins are the smooth, oval hills formed from glacial deposits, and in Ireland they were frequently chosen as sites for early enclosures, offering natural elevation and visibility across the surrounding landscape. What you see here today is a hollow roughly ten metres across at its base and twenty metres at its widest point, sinking somewhere between one and three metres below the pasture around it. Easy to walk past, easier still to misread as a natural dip in the ground.

Ordnance Survey maps from 1842 and again from 1920 both record the site using hachure marks, the cartographic convention for indicating an enclosure or earthwork, showing a circular form approximately thirty metres in diameter. The fact that it appears consistently across both editions suggests it was still a legible feature well into the twentieth century. Since then, the raised bank or wall that would have defined the enclosure has been lost, levelled by the ordinary processes of farming and time, leaving only the interior depression. The original function of such enclosures in the Irish landscape is rarely certain without excavation; they may represent a ringfort, a defended farmstead of the early medieval period, or something older. At Ballyline, no excavation appears to have taken place, and the site remains unclassified beyond the broad term earthwork.