Mynydd Rhiw, 304m above sea level at its highest point, dominates the south-western tip of the Llyn peninsula. The geology of the mountain comprises ridges of hard volcanic rock, interspersed with a finer-grained shaley rock, that was exploited during the Neolithic period for the manufacture of stone tools such as axes, knives and scrapers.

The discovery of the Mynydd Rhiw axe factory was made by the Royal Commission in the late 1950s, during fieldwork for the Caernarfonshire inventory to verify aerial photographs that had revealed a set of three hollows (centred SH 23391 29906), then interpreted as the remains of `round huts?. Close examination revealed the banks surrounding the hollows were composed of debris from stone axe manufacture and subsequent excavation by the Commission in 1958 and 1959 showed these features were not huts but rather the remains of 5 quarry pits, a maximum 15m in diameter, exploiting a rock seam that dipped into the hillside. The hollows had been created by the backfilling of the exhausted quarries, though a series of open hearths placed in them suggested that they might subsequently have provided shelters for the workforce. These remains are now largely obscured by gorse and heather.

A second programme of fieldwork (survey and excavation) on the mountain began in 2005 under the direction of National Museum Wales. This time the focus was on the other (east) side of the mountain (SH 23304 29544), where traces of quarrying and stone axe manufacture, in the form of shallow scoops, hollows and scree have been identified over a 600-metre length of hillside. Here excavation demonstrated that Neolithic people were digging into a drift deposit, up to depths of 2 metres, to extract loose blocks of stone from the soil rather than quarrying the bedrock directly. Radiocarbon-dating suggests that the hill was visited for this purpose from 3,650 BC until about 3,050 BC and that there was also later use of the stone associated with the building of cairns and possible agricultural activity on the mountain.

The extent of the quarrying demonstrated at Mynydd Rhiw has caused a rethink of its role during the Neolithic. Despite the massive amount of quarrying on the hill, only about a dozen axes of the material produced have been found across Wales in Flintshire, Glamorgan and the borders. This suggests that the ridge was exploited primarily to supply stone locally rather than for long-distance trade.

Louise Barker, RCAHMW, July 2015

Sources
Barker L. and Burrow S. 2008 Neolithic Manufacture: The Mynydd Rhiw Axe Factory. In Wakelin P. and Griffiths, R. (ed) Hidden Histories. Discovering the Heritage of Wales. RCAHMW
Burrow, S. 2011 The Mynydd Rhiw quarry site: Recent work and its implications. In Davis, V. and Edmonds M. (ed) Stone Axe Studies III. Oxbow
Houlder, C.H. 1961 The excavation of a Neolithic stone implement factory on Mynydd Rhiw in Caernarvonshire. Proceedings of the Prehistoric Society vol. 27, 108-143.