A rath, as these circular earthen or stone enclosures are known, would originally have served as a defended homestead, its bank and ditch marking the boundary of a family's dwelling and agricultural space. This one measured somewhere between 25 and 30 metres in diameter, a modest but typical size, and it commanded reasonable views eastward and south-eastward over low-lying, wettish ground. That elevated position, useful once for surveying the surrounding terrain, is now about all that survives in any legible form.

The earliest clear record of the enclosure appears on the 1838 Ordnance Survey six-inch map, where it is shown as a circular feature boxed in by field walls. Later map editions already begin to render it as something less coherent, a tangle of oblong and linear shapes that hints at progressive damage. What remains on the ground today bears this out. A field wall running on an east-west axis now cuts straight through the middle of the site, dividing it into two unequal portions. To the north of this wall, the ground holds a barely perceptible undulation that may represent the northern third of the original enclosure. To the south, a sod-covered stone bank traces a broad arc from east-south-east around to south-west, preserving something of the southern curve. The bank is low, roughly two metres wide at the top and no more than three and a half metres at its broadest, with a near-vertical outer face of large stones and boulders that appears to have been reworked at some point and absorbed into a field boundary. Inside the surviving southern arc, cultivation ridges cross the ground in the same east-west direction as the bisecting wall, and a quarried-out hollow roughly 0.7 metres deep has further disturbed the interior. The overall picture is of a site that has been not so much abandoned as gradually cannibalised, its fabric repurposed over generations for the more immediate demands of farming. A second possible rath lies approximately 140 metres to the south, suggesting this part of Castlehill may once have held a small cluster of such enclosures.