It is a fulacht fia, a class of monument found in enormous numbers across Ireland, typically understood as a Bronze Age cooking place where water was heated by dropping fire-cracked stones into a trough. The stones, shattered and discarded after repeated heating, accumulated into a horseshoe-shaped mound around the trough, and it is these spreads of burnt and broken rock that survive at so many Irish sites. At Knockilly, even that modest trace has gone.

The site was recorded on an Ordnance Survey six-inch map from 1937, where it appeared as a circular mound in what was already agricultural land. By the time the monument was formally documented, no visible surface trace remained. The land had absorbed it. This is not unusual for fulachtaí fia as a category; they are low-lying and often ploughed or levelled over centuries of farming, leaving the archaeology intact underground while the surface gives nothing away. What is notable here is simply how completely the Knockilly example has disappeared, reduced to a map reference and a grid coordinate, present only as an entry in the archaeological record of north Cork.