These are cropmarks, the faint signatures that buried features leave on growing crops when dry or wet conditions cause plants above filled-in ditches or compacted ground to ripen at slightly different rates to the surrounding field. The result, seen from altitude, is a ghostly photograph of something that ceased to be a visible structure long ago.

The site was first recorded as a cropmark in aerial photographs taken in July 1970, and again more clearly in July 1989, when three concentric fosses, or ditches, showed up in images revealing the full circular plan. Enclosures of this kind, with multiple surrounding ditches, are known from elsewhere in Ireland and are generally associated with the early medieval period, though without excavation the date and function of any individual example remain uncertain. What the aerial evidence at Templenoe does suggest is a site of some elaboration; a single enclosing fosse was common, but three concentric ones point to something that warranted greater effort, whether for status, defence, or ritual purposes. The outermost of the three ditches has been clipped on its eastern side by a road, which means part of the circuit has been lost to modern infrastructure, though the remainder appears to survive below ground.