The hollow is not a collapse or a wound left by diggers. It sits there precisely, three metres across, sunk about a quarter of a metre below the crest of the mound that encircles it, as if something was always meant to be absent from the middle.

The mound itself is modest by any measure, roughly eight metres north to south and ten metres east to west, and rising on average only 0.35 metres above the surrounding ground. Beneath the grass it is mainly composed of stone, sitting atop a natural limestone outcrop in an area that has otherwise been heavily reclaimed for agriculture. A north-south field boundary cuts straight through the complex, bisecting it with the brisk indifference of generations of farmers who had other concerns. Survey work carried out by Michael Connolly in the Lee Valley area between 1996 and 1997 recorded not just this central mound but a broader scatter of low banks, further depressions, and additional earthworks that had shown up on aerial photographs yet could not be reliably traced on the ground. That gap between what the air reveals and what the earth will confirm is itself suggestive: the visible surface represents only part of what is here, and possibly only a fraction of what was once here. The function of the mound, and of the complex it belongs to, remains unresolved.