The northern banks of the river Boyne in County Meath, Ireland, at a spot called the Bend of the Boyne, are the site of a remarkable concentration of Neolithic tombs dating to the late fourth millennium b.c.e. These include three large passage tombs: Newgrange, Knowth, and Dowth.
At Newgrange a single 19-meter (60-foot) passage leads in from an entrance on the southeast side of a huge mound (some 80 meters [260 feet] across), famously oriented so that the sun shines directly along it, lighting up the central chamber, just after dawn on days around the winter solstice. Each of the other major tombs has two passages. Those at Knowth run deep into the interior from entrances opposite each other, facing more or less due east and west respectively. Dowth has passages of different lengths, both in its southwestern quarter. The longer one runs in from an entrance in the west-southwest, the shorter one from the southwest.
Apart from Newgrange, only the shorter passage at Dowth could conceivably be interpreted as aligned upon the solstitial sun, and the target here is winter solstice sunset rather than sunrise. However, it has also been pointed out that the three monuments, taken together, might have a broader calendrical significance. Each of their five passages is oriented close to sunrise or sunset on a solstice, equinox, or mid-quarter day: that is, upon one of the dates obtained by dividing the year into eight exactly equal parts starting at either of the solstices. This division is reflected in the traditional Celtic calendrical festivals, which fall close to these dates. It is also reflected in the precise alignments upon sunrise or sunset on these dates at many British megalithic sites that were claimed by Alexander Thom in the mid-twentieth century and seemed to imply that a calendar dividing the year into eight equal parts had been in extensive use throughout Neolithic Britain.
However, as later reassessments showed, the archaeological and statistical evidence simply does not support Thom’s “megalithic” calendar, and the idea of any all-pervasive Celtic calendar in later, Iron Age times has proven highly questionable. Astronomical and calendrical practices throughout later prehistory were much more variable and localized. Furthermore, the supposedly calendrical alignments of the Boyne valley tomb passages (Newgrange aside) are not exact. All this suggests that the Boyne valley tombs may have done no more than to fit within a broad general pattern of orientation practice that prevailed locally and perhaps extended to Irish passage tombs further afield. This much would accord with what one finds among local groups of later prehistoric tombs and temples throughout western Europe. Indeed, we need look no further than the sixteen smaller passage tombs that surrounded Knowth in order to see a broad range of passage orientations varying from northeast around through east and south to southwest, but avoiding the northwest and north.
Yet it remains possible that more particular practices relating to the seasons and the skies may show up archaeologically in other ways, as “one-off” phenomena, such as the solstitial hierophany at Newgrange itself. Thus, one of the decorated kerbstones at Knowth resembles a sundial, while another contains a cyclic arrangement of twenty-nine circles and crescents that could be a representation of the phase cycle of the moon.
