By the time anyone thought to look closely, the evidence had almost entirely vanished.

The site appears on the 1838 Ordnance Survey six-inch map, already named Lisnatrap Fort and already planted with fir trees within what is shown as a roughly circular enclosure. The name itself, and the circular form, suggest a rath, the type of ringfort, typically an earthen bank enclosing a homestead, that was built across Ireland from the early medieval period onward. What seems to have happened here is that the original earthwork was later absorbed into the design of a demesne landscape, the kind of managed estate grounds that surrounded an Anglo-Irish country house, and a stone wall was built over the enclosing bank from the north-west to north-east and from south-east to south-west. By the time of the resurvey between 1912 and 1916, the OS 1:2500 plan shows a walled mixed tree plantation rather than anything recognisably ancient. On a site inspection in November 1967, the underlying bank was barely perceptible, with only a scatter of old trees growing along what had once been its perimeter. A return visit in April 1983 found no visible surface trace at all. The site has effectively been erased at ground level, though its circular outline remains readable in aerial photography from 2018.

Lisnatrap Fort is, in the end, a site that exists more convincingly from the air than on the ground. The gradual layering of the record, from possible prehistoric or early medieval enclosure, to ornamental plantation, to bare farmland, makes it a quiet example of how the Irish landscape can simultaneously preserve and obscure what lies beneath it.