Some monuments are remarkable for what they were; this one is remarkable for what it no longer is. On the floor of a northwest-to-southeast valley at Ballyquin in County Waterford, there once stood a second cromlech, a portal tomb, sitting roughly fifty metres east of a surviving example that can still be visited today. The two structures were described as closely similar in form, yet the vanished one appears to have been the larger of the pair, its capstone measuring approximately 4.5 metres by 2.5 metres, with a thickness of around 1.5 metres. That is a considerable slab of stone, and its disappearance is all the more striking for it.

Everything known about this monument comes from just two nineteenth-century sources. Around 1840, the antiquarian John O'Donovan visited the area as part of the Ordnance Survey's fieldwork and noted the structure's presence and general character. A decade or so later, W. R. Blackett described it in the same terms in his 1851 account of Waterford antiquities, adding that one of the two upright portal-stones had already fallen. Portal tombs, sometimes called dolmens, are among the earliest megalithic monuments in Ireland, typically consisting of two or more tall standing stones supporting a large capstone to create a chamber; they date broadly to the Neolithic period. At Ballyquin, even at the time of these early observations, the structure seemed incomplete, with no other supporting stones clearly in evidence, which left some uncertainty about whether it fully qualified as a portal tomb or represented something else entirely. At some point after those visits, the stones were removed altogether, leaving the pasture unmarked and the monument reduced to a footnote in two old journal articles.

The site is recorded on both the 1840 and 1926 editions of the Ordnance Survey six-inch maps, which at least fixes its approximate location on the valley floor. The surviving Ballyquin portal tomb to the west remains accessible and gives some sense of what the lost structure might once have looked like, though the two were never identical, and the larger capstone of the vanished example would have made for a noticeably different silhouette against the Waterford hillside.