Tucked within that later boundary is what appears to be the remains of a cashel, a type of early medieval ringfort defined by a drystone rather than earthen enclosure wall. The inner wall, surviving to roughly half a metre in height and two and a half metres wide, traces a circular area approximately 29 metres across, with what may be an original entrance gap on the southern side. Ten metres of space separates this inner enclosure from the outer estate wall, a gap that suggests the two structures belong to entirely different worlds, even if they ended up sharing the same ground.

The leading interpretation is that when Oldcourt House was built in the nineteenth century, the cashel was absorbed into the new estate's landscaping and repurposed as a tree-ring, a decorative circular planting feature. This was not an uncommon fate for ancient enclosures during the great era of demesne improvement, when landowners reshaped their grounds with formal avenues, planted belts, and ornamental features. The old boundary wall became, in effect, a garden convenience. A low mound of loosely piled stones still occupies the western sector of the inner enclosure, the possible residue of the original structure left undisturbed, or perhaps disturbed just enough to be unrecognisable to a casual eye.