When the Ordnance Survey recorded it in 1837, the cartographers annotated it simply as a "fort", which is the kind of label that covered a multitude of things in nineteenth-century mapping. It may have been the most convenient word available, but it is probably not the most accurate one.

The Down Survey of 1654 to 1656, a vast Cromwellian mapping project that documented land ownership across Ireland after the wars of the mid-seventeenth century, depicted Tyfarnham church standing beside a building on its map of the parish of Leny and Tyfarnan. The accompanying terrier, a written description of parish lands and features, recorded that within the parish were situated "the Hall and Church of Tyfarnan". The church site still exists, about 150 metres to the north of the earthwork, surrounded by its own earthworks. The small rectangular enclosure to the south may be all that physically remains of that hall, its walls long since gone and its outline reduced to a barely perceptible rise in the ground. A further complication sits beneath the question: aerial photography from 2011 reveals that this smaller earthwork appears to sit within the northern quadrant of a much larger, sub-triangular earthwork. Whether that larger feature is a pre-1700 archaeological monument or the result of later land reclamation work has not been established, which means that what looks like one puzzle is, on closer inspection, two puzzles nested inside each other.