That sentence carries more weight than it might first appear, because the replacement was not accidental or natural: between the Ordnance Survey's six-inch map of 1842 and the edition of 1903, a clearly defined circular earthwork, shown with hachures indicating its raised rampart, had been quietly reorganised into a subrectangular agricultural field of almost identical dimensions. The ringfort was not merely abandoned; it was incorporated, its outline repurposed into field boundaries, and then those boundaries too were eventually removed. Today there is no visible surface trace of anything.

A ringfort, sometimes called a rath, was a roughly circular enclosure defined by one or more earthen banks and ditches, used as a farmstead and defensible homestead during the early medieval period in Ireland, broadly from around the fifth to the twelfth century. The one at Monavanshere was a substantial example. Writing in 1939, P. J. Hartnett was able to trace the original rampart running outside the later field fences, and his measurements describe an oval enclosure roughly 300 feet north to south and 280 feet east to west, considerably larger than the approximately 80-metre diameter shown on the 1842 map. That discrepancy likely reflects the difference between the visible central depression and the full outer extent of the earthwork as Hartnett traced it on the ground. There is also a possible souterrain recorded in the interior. A souterrain is an underground passage or chamber, typically stone-lined, associated with early medieval settlements and thought to have served for storage, refuge, or both.

The difficulty now is that the site offers nothing to the eye. The pasture runs flat and unmarked over what was once a substantial presence in the landscape. Its interest lies precisely in that invisibility, in the way the 1842 and 1903 maps, read side by side, make the act of erasure legible across a single generation of agricultural improvement.