CONCENTRIC CIRCLES AT LLWYN-DU BACH, PENYGROES, CAERNARVONSHIRE1 By Dr. GERHARD BERSU, Hon. F.S.A., and W. E. GRIFFITHS, M.A., F.S.A. IN a recent paper on "Hut-circles in North-West Wales," W. J. Hemp and C. A. Gresham2 drew attention to a well-defined type of site which they called concentric circles. They gave them the following definition "The sites so termed consist of a central 'hut-circle' surrounded by one or two more or less concentric circles of walling. Most of those that have so far been noted are built on sloping ground, and the area within the second ring is cut back into the slope at the top and terraced out at the bottom, thus forming a fairly level area on which the central hut is placed Where the rocky nature of the site prevents any extensive excavation into the slope only the central hut itself is so levelled. Some- times there remain the traces of a walled passage-way through the two outer circles, but the low walls of these circles, if they carried no superstructure, can have had little if any defensive value. The size of these circles varies from about 80 to 200 feet in overall diameter, with central huts of 24 to 30 feet internal diameter The amount of cutting back and terracing up may be quite slight [as in the case of Llwyn-du Bach] or rise to 7 or 8 feet according to the steepness of the slope. Such sites seem to be restricted to North-West Wales. None has been excavated so far." The Caernarvonshire Excavation Committee, under the chairmanship of Sir Ifor Williams, decided in the summer of 1947 to excavate such a site. On the advice of Mr. W. J. Hemp, a well-preserved site, Llwyn-du Bach near Penygroes, Caernarvonshire, with two concentric rings surrounding the inner ring, was selected. It had already been surveyed in 1946 by the Royal Commission on Ancient Monuments in Wales and Monmouthshire, and this plan, supplemented with contour-lines at 1-ft. intervals, is reproduced here as Fig. 1.3 The results of a trial excavation in 1947 suggested that a more extensive investigation should be carried out. This was done between March 17th and April 14th, 1948. The funds were provided mainly by the Board of Celtic Studies and the Cambrian Archaeological Association, generous contributions also being made by the Society of Antiquaries, the Prehistoric Society, The Royal Archaeological Institute, the Caernarvonshire Historical Society, and by private 1 The cost of publishing this paper has been partially defrayed by a grant from the Council for British Archaeology. 2 Antiquity, XVIII (1944), p. 183. The results of the excavation showed that surface indications are in general quite reliable, though less so with regard to supposed faces of walls. We have intentionally retained the pre-excavation plan (Fig. 1) without correcting it to correspond with the results of excavation (e.g. stones shown in black on the plan are those presumed to be in their original positions) because it is instructive to see how far even very carefully studied surface evidence can be misleading.