On the 17th of July 1967, an aerial photograph captured what archaeologists call a cropmark, a phenomenon where buried features cause the vegetation or soil above them to respond differently to drought or stress, producing patterns readable only from altitude. What the camera caught was a near-perfect ring, somewhere between ten and fifteen metres across, betraying the outline of a fosse, a ditch, cut into the earth long ago and long since silted and buried beneath the ploughed field.

This kind of feature is known as a ring-ditch, a circular or near-circular ditched enclosure whose origins can vary considerably. Some ring-ditches are the eroded remnants of Bronze Age burial mounds, the surrounding ditch all that survives after millennia of ploughing have levelled any central mound. Others may relate to small enclosures of entirely different function. Without excavation it is rarely possible to say which category applies, and this particular example has not, as far as the record shows, been investigated below the surface. Its diameter places it at the smaller end of the scale, closer in size to a large room than to a field, which adds to the uncertainty about its original purpose. The 1967 photograph remains the primary evidence for its existence.