A residential development now occupies the ground where, beneath the soil, two concentric ditched enclosures once defined a space that people had been returning to, on and off, for thousands of years. The monument was fully excavated under licence 19E0303 in advance of construction, and what the excavation recovered tells a story considerably more interesting than the suburban streetscape that replaced it.

Archaeologist Gill McLoughlin, working for Courtney Deery Heritage Consultancy Ltd. on behalf of Sherman Oaks Ltd., recorded an inner enclosure measuring roughly 36 metres by 29 metres, ringed by a ditch up to 3.2 metres wide and 1.41 metres deep, with no detectable entrance. Around it sat a much larger outer enclosure, approximately 105 metres by 71 metres, its course serpentine and irregular, particularly on the western and southern sides. Radiocarbon dating placed the main period of use between the mid to late 7th century and the late 10th century AD, though earlier activity was also present: a Bronze Age copper-alloy knife blade turned up in the outer ditch, and a yew wood bucket recovered from waterlogged deposits at the base of the inner ditch was dated to between AD 652 and 763. Alongside it came bone comb fragments, an iron weaving tensioner, iron slag, and a tuyere, the nozzle through which air is forced into a forge, all pointing to small-scale domestic and craft activity. Cattle bone dominated the animal assemblage, accounting for 59 per cent of identified individuals, a proportion considered high for the period and suggestive of feasting rather than everyday subsistence. The eastern side of the outer ditch corresponded precisely with the townland boundary between Portmarnock and Drumnigh, a boundary still legible on modern maps.

This enclosure, designated Phase 1C, was not isolated. Two further enclosures had been excavated in the same field in 2016 and 2017, approximately 150 metres to the northwest and 200 metres to the north respectively, and an associated enclosure in the nearby townland of Maynetown has also been identified. Taken together, with their feasting deposits, imported high-status finds, a burial, and an upstanding mound, McLoughlin interpreted the cluster as a possible assembly landscape, that is, a place where communities gathered periodically for purposes social, legal, or ceremonial rather than for permanent settlement. The ground itself is now gone, built over and unreachable, but the excavation archive and McLoughlin's 2022 report submitted to the National Monuments Service preserve what was there.