The ground is level enough, the grass unbroken, the slope gentle and south-facing. Yet somewhere beneath the surface, the ghostly outline of an early medieval settlement persists, invisible to anyone standing in it but legible from the air as a crisp circular cropmark, roughly 35 to 40 metres across.

A rath, or ringfort, is an enclosed farmstead of the early medieval period, typically bounded by one or more earthen banks and ditches. Thousands were built across Ireland between roughly the fifth and twelfth centuries, and while many survive as upstanding earthworks, a significant number have been ploughed or otherwise levelled over the centuries, leaving only buried ditches to betray their presence. At Ballycanew, a single enclosing feature, most likely the remnant of just such a ditch, shows up in an oblique aerial photograph as a cropmark, the slight difference in soil moisture and depth causing the grass above the buried cut to grow at a different rate from the surrounding field. The photograph that captured this, taken as part of the Cambridge University Collection of Aerial Photography and catalogued as BGP 84, is the sole evidence on record for the site's existence.

There is nothing to point a visitor toward this particular field, and nothing to see once there. That is, in its own way, the most telling thing about it. The site belongs to a large and quietly extraordinary category of Irish archaeology: places that are known to exist, that have a presence in the scholarly record, but that offer no visible trace to anyone not looking down from several hundred feet above the ground.