Somewhere west of Mayne bridge in County Dublin, a house once stood, dating to the sixteenth or seventeenth century. Nobody can say exactly where. The structure has left no confirmed trace on the ground, and its precise location remains unknown. What survives is a single piece of cartographic evidence, and the faint suggestion of a life once lived in this corner of north County Dublin.

The evidence comes from the Down Survey, the extraordinary mapping project carried out between 1655 and 1656 under the direction of Sir William Petty. Commissioned in the aftermath of the Cromwellian conquest of Ireland, the Down Survey was designed to quantify confiscated Catholic-owned land so that it could be redistributed to soldiers and adventurers who had backed the parliamentary cause. It produced some of the most detailed maps of Ireland made up to that point, and it is on one of these sheets that a dwelling appears, marked to the west of Mayne bridge in the area known as Maynetown. The record was compiled by researcher Geraldine Stout and uploaded to the national monuments database in August 2011, though even that careful work could not pin down the building's exact position.

For anyone curious enough to visit the area around Maynetown and Mayne bridge, the experience will be one of inference rather than discovery. There is no ruin to inspect, no foundation exposed in a field. The value here is in the landscape itself, and in knowing that the Down Survey map was detailed enough to record modest domestic structures, not just grand estates or fortifications, which tells you something about the ambition of Petty's project. Walking the ground west of the bridge, you are essentially searching for an absence, a location that was considered significant enough to mark in the 1650s but that has since slipped entirely from the physical record.