It is the kind of thing that stops you mid-thought: an ancient earthwork absorbed into an industrial estate, still present, still measurable, still there.

The mound at Coolock is a round-topped earthen structure roughly 19.20 metres in diameter and 4.80 metres high, recorded by Morris in 1939 and noted again by Dillon Cosgrave in 1977. Its low-lying, streamside position is worth pausing on. Mounds of this type in the Irish landscape can belong to a range of traditions, from burial mounds raised during the Bronze Age to later medieval mottes, which were earthen platforms built by Anglo-Norman settlers as foundations for timber fortifications. Without excavation, it is difficult to say with certainty which tradition this one belongs to, and the notes compiled by archaeologist Geraldine Stout do not assign it a definitive function. What they do confirm is that it survives, with trees now growing from its crown, within the perimeter of what was the Cadbury's manufacturing facility in Coolock.

Access to the mound is not straightforward for the casual visitor, given its location within a private industrial site. The trees planted on top are visible as a slightly incongruous clump of green if you happen to know where to look, but there is no public path or interpretive marker. Those with a serious interest in early Irish earthworks, or in the archaeology of the north Dublin suburbs, would do well to consult the National Monuments Service records before making any approach. The stream beside which it stands has likely shaped this corner of the landscape for far longer than the factory ever has.