No earthwork rises above the grass, no stones mark its circuit. What gives it away is the crop itself: in dry summers, the buried ditch, or fosse, that once defined this roughly seventy-metre-wide enclosure causes the plants above it to grow differently from those on either side, producing a faint discolouration readable only from the air. It was precisely this kind of cropmark that revealed the site on aerial photographs taken on 16 July 1971.

A fosse is simply a ditch dug into the ground, often part of an enclosure that would have been defined by a bank on its inner edge. Here, three sides of the enclosure appear relatively straight, while the southern side curves inward, giving the whole a sub-rectangular rather than perfectly geometric shape. What makes the Grevine site particularly telling is how the surrounding landscape has quietly accommodated it over the centuries. A field boundary already present on the first Ordnance Survey six-inch map of 1839 bends noticeably westward to avoid cutting through the monument, a small but significant gesture suggesting that whoever farmed this land in the nineteenth century still recognised the ground as in some way set apart. By the time a revised map was produced in 1947, a house had been built into the north-western angle of the enclosure, with an associated plot extending southward through its western half. The monument had become a building plot, though the older field boundary continued to respect its edges. Around fifty metres to the south, three parallel boundaries of their own run north-west to south-east for approximately 140 metres, also visible only as cropmarks, hinting at a wider pattern of early activity in the surrounding fields.