A rath is a ringfort, typically an early medieval enclosed settlement defined by one or more earthen banks and ditches, and this one is built to a considerable scale: nearly fifty metres across, with a double-bank arrangement and an intervening fosse, the term for the ditch between them. Traces of stone-facing survive on the inner surfaces of both banks, suggesting that whoever built it invested real effort in its construction. A causewayed entrance gap on the eastern side, where the ditch is bridged to allow passage, is still legible in the landscape.

What makes Earlspark particularly interesting is what geophysical survey has added to the picture. Work published by Beglane in 2014 identified a further inner fosse not visible above ground, and what may be the footprints of buildings within the interior, neither feature apparent from surface inspection alone. More intriguing still, Beglane proposed that the rath was likely modified and reused when a high medieval deer park was established in the area. Deer parks were aristocratic enclosures, common among Anglo-Norman lords from the twelfth century onwards, used for hunting and the keeping of game. The suggestion is that an existing prehistoric or early medieval structure was repurposed to serve the needs of a later, very different kind of landowner. The surrounding landscape reinforces the sense of a place that was repeatedly found useful: another rath lies roughly 325 metres to the south-west, an enclosure sits about 95 metres to the south, a hillfort approximately 75 metres to the west, and a standing stone around 460 metres to the south-south-west. This is not an isolated monument but one node in a dense and layered archaeological neighbourhood.