The circular enclosure at Glashina, in County Wicklow, announces nothing at all. On the ground, there is simply a field on a gentle east-facing slope, unremarkable in every direction. The site exists, for most practical purposes, only from the air, where it appears as a cropmark, the faint differential in how grass or grain grows over buried features betraying a ring roughly thirty metres across that would otherwise be entirely invisible to anyone walking past it.

Cropmarks form when buried archaeology affects the soil above it, causing vegetation to grow slightly taller or shorter, greener or yellower, than the surrounding area. In dry summers especially, these variations can be read clearly from aerial photographs, and it is through exactly this method that the Glashina enclosure came to be recorded. The site is circular, which in an Irish context often suggests early medieval activity, though enclosures of this type were built across a wide span of prehistory and into the early Christian period. A circular enclosure, sometimes called a ringfort or rath when its earthworks survive, was typically a farmstead boundary, defined by a bank and ditch that protected a household and its livestock. At Glashina, no bank or ditch is visible; whatever once defined the perimeter has been levelled so thoroughly that only the buried traces remain to cast their shadow in the crop above.