Among the monuments that once dotted this landscape was a boulder circle, a ring of large standing stones forming an enclosure roughly 13.7 metres in internal diameter, with no detectable central structure remaining even when it was first recorded. It is a monument that was already partly a mystery before it was entirely erased.

When the antiquarian George Petrie visited the site in 1837, nine boulders of the circle were still in place. Passage tomb cemeteries of this kind, where megalithic chambers and enclosing stone circles cluster together across open ground, are among the oldest monumental landscapes in the world, and Carrowmore is one of Ireland's largest examples. The particular monument Petrie observed sat within that wider complex, though whatever central feature it may once have held, whether a burial chamber, a cairn, or something else altogether, had already vanished by his time. Within fifty years of his visit, the remaining stones were gone too. By 1888, when the local historian W. G. Wood-Martin surveyed the area, he could find no trace of them whatsoever. The cleared ground left nothing to excavate, nothing to date, and no way of recovering what had stood there.