At Knocknashammer in County Sligo, a low earthen mound once stood to the south-east of a known prehistoric barrow, a type of burial monument typically constructed during the Bronze Age as a rounded earthen or stone-covered cairn over the remains of the dead. The mound in question was modest, roughly 1.5 metres high and somewhere between 8 and 10 metres across, and was considered a possible second barrow associated with the same site. It has since been removed entirely, leaving nothing visible above or below ground.

The neighbouring barrow was excavated by M. A. Timoney in 1977, and it was that work which drew attention to the smaller mound nearby. Whether it truly was a second funerary monument was never established with certainty before it disappeared. Timoney later confirmed that the removal had been total, with no surviving archaeological trace. The site at Knocknashammer therefore occupies a peculiar category in the Irish archaeological record: a place noted not for what was found, but for what was there, was suspected to matter, and was then lost before anyone could be sure.