Somewhere beneath the fields at Sion in County Kildare, a circle is waiting. It does not announce itself with earthworks or upstanding masonry; there is nothing to see at ground level. The only evidence of its existence came on a summer's day in 2018, when aerial photography caught a faint circular stain in a crop, roughly ten metres across, the kind of ghost that only shows up in certain conditions of heat and growth.

What the image captured is known as a cropmark, a phenomenon where buried features influence the vegetation above them. Ditches cut into subsoil tend to retain more moisture, producing lusher, taller growth that reads from above as a darker stripe or, in this case, a ring. The site at Sion appears to preserve the outline of a ring-ditch, a type of monument typically associated with prehistoric funerary or ritual activity. Such features are often the eroded remnants of a burial mound, where the encircling ditch that once defined the monument survives in the soil long after any central mound has been ploughed flat. At approximately ten metres in diameter, this is a modest example, but size is rarely the point with cropmark archaeology. The circle was identified from Google Earth imagery photographed on 28 June 2018, and the find was subsequently compiled by Caimin O'Brien on the basis of details provided by Jean-Charles Caillère.