It bends outward for no obvious agricultural reason, traces a short arc, and then straightens again. That curve is almost certainly the last visible trace of an earthwork enclosure at Mallardstown Great, a monument that has otherwise been completely levelled and absorbed into the farmed landscape around it.

The enclosure was recorded on the first edition Ordnance Survey six-inch map of 1839, where it appeared as a polygonal form, meaning it had a number of roughly straight sides rather than a smooth curve. By the time the OS returned for the 1948 revision, the plan had softened in the record to a roughly circular shape, approximately 43 metres in overall diameter, surrounded by a wide, deep fosse. A fosse is simply a ditch, typically dug to define or defend a site, and in Irish archaeology such enclosures are found across a broad range of periods and functions, from early medieval farmsteads to later ceremonial or territorial boundaries. The specific origins of this one are not recorded. At some point between 1948 and the early twenty-first century, the interior was levelled, erasing whatever earthwork had survived above ground. Satellite imagery captured between 2005 and 2012 still showed the fosse as a faint cropmark, except along the southern and south-south-western edge, where the field boundary had been adjusted to follow the old perimeter, preserving its line even as it obscured the ditch beneath.