Somewhere beneath the farmland of Tyrrellstown in County Kildare, a rectilinear earthwork enclosure lies largely invisible at ground level, its outline legible only from the air. That geometry, a roughly rectangular form with an internal division running through it, is the kind of trace that the Irish landscape occasionally gives up when the angle of light and the season conspire to throw up crop marks or soil shadows across otherwise featureless fields.

The enclosure came to light on 13 July 1990, when Dr. Gillian Barrett was conducting an aerial photographic survey of the area. The resulting photograph, catalogued as GB90.BB.26, captured the rectilinear outline and its internal division clearly enough to record the site formally. Rectilinear enclosures of this kind in Ireland are associated with a range of periods and uses, from early medieval ecclesiastical or agricultural enclosures to prehistoric or later settlement boundaries, though without excavation it is rarely possible to assign a confident date. What the internal division suggests is some form of deliberate spatial organisation within the enclosure, separating one zone from another for purposes that remain unknown. The Kildare landscape, historically well settled and intensively farmed, holds many such buried or semi-buried features, most of them never excavated and known only through the distant eye of aerial photography.