The fort is oval rather than the more commonly illustrated circular form, measuring roughly fifty metres east to west and thirty metres north to south, and what makes it worth pausing over is precisely its state of partial survival: not dramatic, not complete, but readable, like a sentence with a few words worn away.

This is a rath, a type of enclosed farmstead typically dating from the early medieval period in Ireland, roughly the fifth to twelfth centuries. A rath was defined by one or more earthen banks and a fosse, which is a ditch, usually dug to provide the material for the bank itself. The enclosure would once have contained a dwelling and associated farm structures, and the surrounding earthworks served as much as a marker of status as a practical boundary. At Marblehill, two banks and an intervening fosse were constructed, which placed this example slightly above the single-bank norm and suggests the original occupant was a person of some local standing. The inner bank remains visible for most of its circuit, though the south-eastern arc has been broken by several gaps. The fosse can be traced all the way around, but the outer bank survives only on the south-western and north-western sides, the rest having been lost to centuries of agricultural use and, more recently, to the planting of the conifers now growing inside the enclosure itself.

A pathway cuts through the monument at both its northern and southern sides, which means a visitor walking through the plantation will pass directly across the earthworks rather than around them. The fort is not set apart or signposted in any dramatic way; its significance lies in learning to read the ground underfoot, the slight rise of the inner bank, the hollow of the fosse running beside it, and the realisation that the trees filling the interior are growing where a family once lived, at some point in the better part of a millennium ago.