Yet this is precisely what archaeologists encountered on the eastern edge of a sewer pipeline trench at Portmarnock in the summer of 2016. The feature is what archaeologists call a burnt mound, a type of site found widely across Ireland and Britain, typically consisting of a mound of heat-shattered stones discarded beside a trough or pit used for heating water. They are among the most common later prehistoric monument types in Ireland, and among the least celebrated.

Excavation of the site took place over five days in late July 2016, led by archaeologist Gill McLoughlin of Courtney Deery Heritage Consultancy Ltd., on behalf of Sherman Oaks Ltd. The pit itself measured 5.2 metres northwest to southeast and 2.4 metres across, with the narrower southeastern end forming a shallow step, roughly 0.43 metres deep, that likely served as an access point. The wider northwestern end reached a depth of at least 1.2 metres, though excavators could not reach the base at the centre because groundwater was flowing in too quickly from below. Five distinct layers of fill were identified inside. The deepest contained alder charcoal, burnt stones, seashells, and occasional animal bone. A radiocarbon date from that basal layer returned a calibrated range of BC 2434 to 2051, placing activity here firmly in the Early Bronze Age, somewhere between four and four and a half thousand years ago. Above it, the main fill held abundant burnt stones, more shells including razor clams, a flint flake, and bone from a calf. The interpretation offered by McLoughlin is that stones were heated in a fire and then used to bring water to temperature in a trough nearby, with the spent material eventually tipping back into the waterhole once it fell out of use.

The site itself is no longer visible; it was excavated in the course of a pipeline development along Station Road, Portmarnock, and the trench extended beyond the limits of the pipeline corridor, meaning part of the pit remained unexcavated. It is possible that further traces of the associated burnt mound survive outside the pipeline corridor. The finds and the full excavation report, submitted to the National Monuments Service, are catalogued under licence 16E0101. For anyone interested in the broader archaeology of the area, the site is a reminder that the suburban north Dublin coastline has a considerably older story beneath it than the housing estates and road schemes that now define the surface.