Somewhere on the western bank of the River Liffey, within the old woodland fringe of Leixlip Demesne, there is an earthen mound that the Ordnance Survey mapmakers never saw fit to record. Or perhaps never noticed. It sits in a narrow strip of trees between the river and open pasture, overgrown and low to the ground, nearly circular in plan, measuring roughly 23 metres across at its base and rising to about two metres at its highest southern point. What makes it quietly anomalous is that flat, levelled top, some nine metres across, the kind of feature that suggests deliberate construction rather than natural accumulation of soil.

The mound's existence is known largely because of a single estate map, undated but attributed to the late eighteenth or nineteenth century, held in the National Library of Ireland. That map shows the mound skirted along its northern edge by a curving field boundary, a boundary that does appear on the first edition Ordnance Survey six-inch map of 1838 and again on the revised edition of 1939. The mound itself, however, was never plotted on any edition of the OS maps. It is the persistence of that curved boundary line, hugging the northern arc of something the surveyors did not formally acknowledge, that preserves the faint outline of the feature across nearly two centuries of cartographic record. What the mound originally represented, whether a burial monument, a platform mound associated with early medieval settlement, or something connected with the later demesne landscape, remains an open question. Platform or flat-topped mounds of this kind in Ireland are often associated with early medieval activity, sometimes serving as the bases for timber structures or markers of territorial significance, though without excavation any interpretation here is speculative.