Somewhere beneath the fields of County Laois lies the ghost of a subcircular enclosure, roughly 70 metres across at its widest point, which has left no trace above ground whatsoever. No earthwork, no ridge, no scatter of stone. The site exists now only as an absence, readable not by walking the land but by flying over it.

The enclosure first appears on the Ordnance Survey six-inch map of 1841, recorded by the cartographers of that remarkable early Victorian survey of Ireland who documented features that were already, even then, disappearing from the landscape. What exactly it enclosed, and when, is not recorded. Enclosures of this general type are among the most common archaeological forms in Ireland, frequently associated with early medieval settlement, though without excavation the specific date and function of this one remain open questions. The clearest evidence for its existence comes from aerial photography, where it registers as a cropmark. This is a phenomenon that occurs when buried ditches or banks, long since levelled, affect the growth of crops above them. In dry summers, the differential moisture retained by the filled-in soil of an ancient ditch can cause the plants overhead to grow taller or greener, tracing the outline of a vanished structure with surprising precision. In the case of Borris Great, that outline is subcircular and substantial, suggesting something that once mattered enough to require a boundary of considerable scale.