A circular enclosure roughly forty metres across, its outline formed by a wide ditch known as a fosse, approximately five metres in width, emerges as a faint cropmark on aerial photographs. Cropmarks appear when buried features influence the growth of vegetation above them, causing subtle differences in colour or height that are invisible at ground level but readable from altitude. A possible outer, narrower enclosure may also be detectable, hinting that what survives is the ghost of a more elaborate structure than the surface suggests.

This is almost certainly the remains of a rath, the Irish term for a ringfort, a type of enclosed farmstead that was the most common form of rural settlement in early medieval Ireland, typically dating from around the sixth to the twelfth century. Ringforts generally consisted of a roughly circular area surrounded by one or more earthen banks and ditches, enclosing a house and associated outbuildings. The double-enclosure arrangement suggested here, with a wider inner fosse and a narrower outer feature, was not unusual for sites of some local significance. The landscape at St. Margarets is described as level, which would have made it well suited to agricultural life; flat ground required less effort to enclose and offered workable soil. That so little is now visible on the surface indicates centuries of ploughing and land use have gradually erased the upstanding earthworks, leaving only these faint impressions beneath the topsoil.