It is a fulacht fia, a type of prehistoric cooking site found in considerable numbers across Ireland, typically identified by a horseshoe-shaped mound of burnt and fire-cracked stones. The working theory is that these sites were used to heat water in a trough, perhaps for cooking, bathing, or other purposes, by dropping stones heated in a nearby fire directly into the water. The stones crack and splinter with repeated use, and it is the gradual accumulation of this spent, blackened material that forms the characteristic mound.

The Shanakill mound was recorded on the Ordnance Survey six-inch map of 1938, marked simply as a mound without further elaboration, which is how many such sites passed through the twentieth century, noted but not fully understood. The boggy, waterlogged ground that surrounds it is, in a sense, exactly where you would expect to find a fulacht fia. These sites cluster near streams and marshy areas, and the wet ground that makes them so awkward to reach today is likely part of the reason they were chosen in the first place. The area is currently noted as inaccessible, and the mound sits in the kind of landscape that discourages casual investigation.