The feature is a ring-ditch, the term used for a roughly circular or oval ditch cut into the ground, often all that survives of a prehistoric burial monument after centuries of ploughing have levelled whatever mound or earthwork once stood above it. This one left no surface trace at all.

It came to light on the 3rd of August 1996, when aerial photography over the area recorded a circular cropmark on the gently south-facing slope where the field sits under tillage. Cropmarks form when buried features, ditches that were once dug and later filled, or foundations that interrupt the natural soil, affect the growth of whatever crop is planted above them. Over a buried ditch, where the soil retains more moisture and nutrients, plants tend to grow taller and stay greener longer; from the ground you see nothing out of the ordinary, but from above, the pattern becomes legible as a distinct shape against the surrounding crop. The ring-ditch at Ballydine survives in exactly this way, preserved only as a difference in how the barley or wheat grows on a summer afternoon when the light and the season are right.