In a tillage field near Rathcoffey in County Kildare, there is an enclosure that has never been excavated, never been mapped on the ground, and may never have been noticed at all were it not for the particular way crops grow above disturbed soil. The site exists, for practical purposes, only as a cropmark, a subtle variation in the colour and height of growing plants that betrays the presence of a buried fosse, or ditch, beneath the surface. Where a ditch was cut into the earth in some earlier century and later filled in, the soil retains more moisture and nutrients than the surrounding ground, and crops planted above it grow fractionally taller and greener. From ground level, nothing is visible. From the air, or from satellite imagery, the difference becomes legible as a faint outline in the field.

This particular outline is oval, running approximately forty metres on its north to south axis and thirty-four metres east to west, dimensions that place it comfortably within the range of the ringfort tradition that was widespread across Ireland during the early medieval period, roughly the fifth to the twelfth centuries. Ringforts, which served as enclosed farmsteads, were typically defined by one or more earthen banks and ditches, and thousands survive as upstanding earthworks across the Irish landscape. Many more do not survive above ground at all, having been ploughed flat over the centuries of intensive agriculture. The Rathcoffey site was first reported by Jean-Charles Caillere, and its presence was confirmed through Google Earth aerial imagery captured in March 2020, where the cropmark of the enclosing fosse could be faintly traced against the surrounding tillage.