A ringfort, or cashel, the term used specifically for a stone-built enclosure rather than an earthen one, survives at Lyle as a slightly raised circular platform roughly twenty metres across. What makes it quietly odd is that at some point, farmers building field walls simply continued along the existing bank, incorporating the ancient boundary into their own, so that from the east around to the south-south-west, the prehistoric stonework and the modern walling are one and the same structure.

The enclosure is formed by an irregular bank of rubble limestone, about two and a half metres wide and surviving to an internal height of somewhere between thirty and fifty centimetres. There is no fosse, the defensive ditch that often runs outside an earthen ringfort, which is typical of stone cashels, where the material for the wall was quarried elsewhere or gathered from the surrounding ground rather than dug up on site. The original entrance, a gap of around one point seven metres, is still readable on the north-west side of the bank, its width just sufficient to admit a person or a small animal. Ringforts of this type were generally built during the early medieval period, roughly the fifth to the twelfth centuries, and served as enclosed farmsteads for a single family or small household, the bank offering as much a statement of status and boundary as any serious military defence.