This mark is barely visible on the LIDAR and cannot be seen on the ground.
There are several possibilities for this feature. The magnetometry survey showed strong indications of the remnants of a stone building. The initial thought was that this could be the site of Carham Tower. A tower at Carham is noted in a 1415 survey of defensive buildings just prior to Henry V’s Agincourt campaign.
It is the expected shape, size and position for such a building. There is the faint mark of a track leading from here to the river crossing. This mark is not visible at ground level. It can be seen on LIDAR but is barely distinguishable on the drone footage.
Another explanation is the square is a part of the remains of the Augustinian Priory