On the eastern slope of Boston Hill in County Kildare, a cluster of ancient furnace pits curves in a careful arc around the hillside, arranged precisely to keep their backs to the prevailing south-west wind and their openings turned towards the sun. It is the kind of deliberate, practical thinking that only becomes visible when you know what you are looking at, and this particular site only came to light at all because a quarry needed to expand its footprint.

In 2001, archaeological monitoring of topsoil-stripping on the eastern slope of Boston Hill, which rises to around 538 feet above sea level, uncovered remains across seven separate areas. The most revealing of these, covering roughly 3,750 square metres, contained at least 28 features, many of them connected to metalworking. Large pits showed signs of burning around their edges and were filled with charcoal-rich soil, along with substantial pieces of both iron and copper slag, the glassy waste material left behind after ore is smelted. The full range of metalworking activity appears to be represented: pit furnaces, smelting furnaces, and charcoal-burning pits. A terminus post quem is a dating technique that establishes the earliest possible date for a deposit based on the youngest material found within it, and here the iron slag places the site no earlier than the Iron Age. But because similar smelting methods continued in use well into the medieval period, the features could belong to almost any point between 500 BC and AD 1500. No pottery was found to narrow that window further. The arc-like arrangement of the features along a single contour line is not accidental; whoever worked here understood the relationship between airflow, heat, and position on a slope.

Most of the archaeological areas identified in 2001 were expected to remain undisturbed by quarrying activity for some decades, meaning much of what was found still lies where it was left, sealed beneath the hillside.