Wedge tombs are a distinctive type of megalithic passage tomb found all over Ireland, but mainly in the west. Over five hundred examples are known, and while they vary widely in size, they do have a defining characteristic: a trapezoidal central chamber, its sides formed by two lines of large, upright stones (orthostats), which is wider and higher toward the entrance end, forming a wedge shape. The bulk of wedge tomb construction took place in the second half of the third millennium b.c.e., placing them chronologically toward the end of a rich tradition of Neolithic tomb construction in Ireland.
The other property that confirms the wedge tombs as a useful category of monuments is the strong consistency in their orientations. Nearly all known examples face the western arc of the horizon, with the majority facing southwest. It is unusual to have such a clear preference for westerly orientation among a group of Neolithic tombs, let alone such a substantial one. The only other example in Britain or Ireland is the few dozen Clava cairns of northeast Scotland. The fact that the Clava cairns also seem to represent a late development suggests that a strong predilection for westerly/southwesterly orientations only developed toward the end of the Neolithic. A similar preference is evident in the orientations of the axial stone circles of southwest Ireland, a region where there is a major concentration of wedge tombs, as well as among the recumbent stone circles of northeast Scotland, which occupy an area close to that where the Clava cairns are found.
What is the astronomical significance of the wedge tombs? Viewed in the context of groups of later prehistoric temples and tombs found all over western Europe, their pattern of orientation fits the “sun descending or setting” model. In other words, each tomb was oriented upon a position where the sun was seen either to set, or to be descending in the sky, on a significant day—perhaps the day on which construction was begun. However, there is one well-studied example that provides tantalizing evidence of more particular concerns. This is the tomb of Altar, situated on the south coast of the Mizen peninsula at the very extreme of southwest Ireland, close to the village of An Tuar Mor (Toormore).
The Altar tomb commands a clear view down toward the tip of the Mizen peninsula, and is directly oriented upon the conspicuous Mizen Peak, which forms a distinctive pyramid shape on the horizon some twelve kilometers (eight miles) away. Added to this, the tomb’s orientation may have had a calendrical significance. As was first pointed out by Boyle Somerville, who surveyed the monument in 1931, it is oriented upon the position of sunset within a couple of days of February 4 and November 5. These are two of the mid-quarter days, which along with the solstices, equinoxes, and the other two mid-quarter days divide the year into eight equal parts. This interested Somerville because the November date corresponded to the festival of Samhain in the Celtic calendar.
The problems with this interpretation apply to all supposed equinoctial and mid-quarter-day alignments, many of which were highlighted in reassessments of the “megalithic” calendar proposed in Britain by Alexander Thom. On the other hand, an intriguing aspect of Altar is the existence of archaeological evidence that suggests a sequence of ritual activity stretching from around 2000 b.c.e. up to at least the first century c.e. This evidence might support the argument of continuity of tradition into “Celtic” times.
However, Altar does not seem to be typical even of the wedge tombs in its immediate vicinity, at least to judge from an analysis of nine other wedge tombs in the Mizen peninsula. Even the impressive topographic alignment appears to be a “one-off.” This means that, as with other single instances among groups such as the solstitially aligned axial stone circle at Drombeg, one must continue to wonder whether the alignments could have arisen fortuitously rather than intentionally.
