That modest irregularity in an otherwise straight boundary is all that now marks a site that appeared on Ordnance Survey maps for nearly a century, was still visible to researchers in the late 1930s, and was gone within a few decades of that.

A ringfort, or rath, is a roughly circular enclosure defined by one or more earthen banks and ditches, typically built during the early medieval period as a farmstead or place of domestic enclosure. The Kilcullen example was recorded on the six-inch Ordnance Survey maps of 1842, 1904, and 1940, each time shown as a circular enclosure of approximately 25 metres in diameter, sitting in rough grazing land. By 1939, when P. J. Hartnett described it, the site was heavily overgrown and already had a drain cut through it, though its circular form of around 68 feet across was still legible in the landscape. Sometime around 1978, according to local information, it was levelled entirely.

What makes this site quietly instructive is how long it persisted on paper after it had become difficult to read on the ground, and how quickly it vanished once the decision was made to clear it. The westward kink in the field fence, preserving the ghost of the old bank's curve, is the kind of detail that rewards anyone with an eye for what farmland is quietly remembering.