The medieval settlement at Portmarnock, on Dublin's north coast, belongs to that category. Where a late medieval village once spread across the soil near Station Road, a residential development now stands. The monument is gone. What remains is the paperwork, and the paperwork turns out to be remarkably revealing.

The site came to light almost by accident in 2016, during monitoring works for a drainage feature associated with an earlier phase of development. What appeared at first to be a modest find was soon understood as the eastern edge of a much larger medieval settlement, part of which had already been excavated by C. Moriarty in 2008 under licence 08E0376. That earlier dig had identified six well-defined property plots with associated yard areas and wells, and dated the main period of occupation to the 16th and 17th centuries. The 2018 excavation, carried out under licence 18E0016 by Gill McLoughlin of Courtney Deery Heritage Consultancy Ltd. on behalf of Sherman Oaks Ltd., extended the picture considerably. In the southern part of the site, the L-shaped foundation of a stone structure was uncovered, with a keyhole-shaped oven set into the wall. Charred cereal retrieved from a founding deposit in that structure returned a date range of 1275 to 1386 AD, pushing the origins of settlement activity back to the late 13th century. The main north-south ditch running through the site dated to between 1420 and 1454 AD. Among the finds recovered were large quantities of Dublin-type and Leinster Cooking Ware, moderate amounts of animal bone, and a substantial assemblage of plough pebbles, smooth stones used to clear fields before ploughing, whose presence in the eastern area suggested that this part of the village had shifted from domestic use to agricultural use at some point after initial occupation. McLoughlin's interpretation was that the settlement had begun in the east during the 13th century and gradually extended westward over time. A separate area of the development lands also yielded a burnt mound trough, a type of prehistoric cooking site associated with heated stones and water, dated to the early Bronze Age, between 2135 and 1920 BC.

There is nothing to see at this location now. The excavation was completed in advance of development under planning reference ABP 300514-17, and the site was built over on completion. The value of knowing about it lies not in any visit but in understanding how much can be recovered, and then erased, within a few years. The full excavation report was submitted by Courtney Deery Heritage Consultancy Ltd. to the National Monuments Service, where the record of what once lay beneath this corner of north County Dublin is preserved.