The enclosure at Harristown in County Dublin was spotted as a cropmark on a 1971 aerial survey, reference FSI 462/1, its outline betrayed by the way grass and soil respond differently above buried ditches during dry summers. Cropmarks form when buried features, such as filled-in ditches or the remains of walls, cause the vegetation above them to grow at a slightly different rate or colour from the surrounding land, creating patterns that become readable only from altitude. At ground level, there is nothing to see at all.

The enclosure is roughly circular and measures approximately 35 metres in diameter, defined by a single ditch. Its form is consistent with a ringfort, the term used for the enclosed farmsteads that were built across Ireland in their thousands during the early medieval period, roughly between the fifth and twelfth centuries. A ringfort typically consisted of a raised circular area surrounded by one or more earthen banks and ditches, serving as a defended farmstead for a family and their livestock. Whether this particular example dates to that period has never been confirmed by excavation. Geraldine Stout, who compiled the record, noted that it may be a levelled ringfort, meaning any upstanding earthwork had already been flattened before the site was recorded. The subsequent expansion of Dublin Airport buried it entirely beneath the runway infrastructure.

There is, in a straightforward sense, no way to visit this site. It lies under active airport infrastructure at Dublin Airport and is inaccessible to the public. What makes it worth knowing about is precisely that inaccessibility, and what it illustrates about how archaeological sites are recorded and then lost. The 1971 photograph remains the only documentation of the enclosure's existence, and no further survey or excavation has taken place on the site. For anyone interested in the archaeology of the Dublin region, the record is held in the national Sites and Monuments database, where the cropmark photograph offers the clearest, and only, view of what once lay in this low-lying pasture north of the city.