It does not interrupt the soil, does not form a bank or ditch, and casts no shadow. It exists, as far as ground-level observation is concerned, not at all. And yet on the 15th of July 1970, a camera mounted in an aircraft recorded it with quiet precision.

The feature is a cropmark, a phenomenon that occurs when buried archaeology influences how crops grow above it. Buried ditches or disturbed soil retain moisture differently from the surrounding ground, and in dry conditions the difference shows up in the colour and height of the crop overhead. From the air, patterns invisible to anyone standing in a field suddenly resolve into lines, curves, and enclosures. In this case, the photograph, taken as part of the Cambridge University Collection of Aerial Photography, revealed a linear east-west field boundary sitting on the crest of a terrace along the foothills of higher ground to the north, with open plain falling away to the east and south. The boundary appears to cut through the northern quadrant of two enclosures nearby, suggesting it belongs to a different phase of activity than the enclosures themselves, laid down at some point when the arrangement of the landscape was being reorganised, the earlier circular features already abandoned or forgotten by whoever drew this new line across the ridge.