The structure is a cist, a type of stone-lined grave box used in prehistoric Ireland, typically formed from carefully arranged slabs to enclose the remains of the dead. This one is unusually large: nine metres long and just under a metre wide, built from limestone blocks and originally covered by a burial mound. That mound is gone now, absorbed into the landscape of suburban development, and the cist itself is not visible at ground level.

The discovery was made during house construction work in 1897, when the chamber was exposed and subsequently noted in the archaeological record. References by both Shearman and the antiquarian T. J. Westropp place it firmly in the documented literature of Irish prehistoric sites, with Westropp recording the mound covering as late as 1922. The use of limestone in its construction is a notable detail: limestone is not the most locally abundant stone on the Howth peninsula, which is dominated by quartzite and other harder rocks, suggesting either deliberate sourcing of material or the reuse of available stone from elsewhere. Whether the cist held a single burial or multiple interments, and from what period precisely it dates, is not recorded in the surviving notes.

For anyone visiting Howth with an interest in its deeper past, this site presents something of an exercise in archaeological imagination rather than direct observation. There is nothing to see at ground level, and no marker signals its presence. Its location within an area that underwent residential development in the late nineteenth century means it now sits in an ordinary streetscape, invisible to anyone passing by. The value of knowing it exists lies less in visiting a specific spot and more in the reminder that the familiar topography of a Dublin coastal suburb can conceal structures of considerable age and scale, going quietly about the business of being ancient beneath the foundations of the houses built above them.