The work of Alexander Thom has had a profound effect on the way that many scholars, myself included, look at megalithic civilization. Indeed, it is difficult to imagine that the homogeneity of methodology and purpose, the precision of calculation and observation, and the likely use of a shared standard of measure do not point to a complex network of communicating civilizations, cohesive in certain ways despite the absence of any central power. The archaeologist Edward Mackie (1977, 1981, 1997), basing his work on Thom's findings, developed this idea into a comprehensive theory that frames ancient astronomical activity in a social structure of megalithic builders. Mackie maintains that there is sufficient archaeological evidence at Skara Brae, to name just one example, to hypothesize the existence of a hierarchical social structure at the top of which was an elite class of astronomer-priests, for lack of a better term, whom he likens to Mayan priests (see Chapter 8). They would have had their own residences, as well as spaces where they would teach their apprentices, an example being the "guest house'' at Skara. The level of knowledge possessed by these individuals was necessarily high, as Mackie demonstrates by evoking the studies of Thom.
Mackie's thesis sounds convincing, and I will explain why in the more general context of Chapter 15. Nonetheless, in the 1980s and 1990s, the work of Thom and, by extension, Mackie's interpretation of it were subjected to heavy critical revision, exemplified in a volume published in honor of Thom, Records in Stone (Ruggles 1988), which contains a number of contributions that are critical about many aspects of Thom's work.
The position from which Thom's work was criticized holds that he had overestimated the technical capacities of megalithic builders grossly enough as to have upgraded a "symbolic'' interest in the sky to scientifically based astronomical practices. In particular, Clive Ruggles (see Ruggles 1999 and the references cited therein) rigorously reexamined many of the sites studied by Thom. When the new measurements are plotted on a histogram, Thom's ""peaks,'' which indicate noteworthy alignments, are dramatically blunted, the science of the megalithic builders shrinking along with them to become a matter of "purely symbolic interest.'' Lying at the root of these discrepancies is, for instance, the fact that Thom occasionally committed technical errors (understandably, given that he studied thousands of sites). But the discrepancies are mainly owed to an "amplification" effect resulting from the data selection criteria used along with the involuntary prejudices intrinsic to such choices. This effect can manifest itself in a number of ways. For example, if there are five possible horizon alignments in a group of megaliths and two prove to be astronomically significant, recording only these two gives the site a statistical weight that it would not have if all five were recorded. If an alignment incorporates a monolith 2 meters wide, the direction it defines will change (and can be made to appear more or less accurate astronomically) if the line is run through the center as opposed to off of the upper left or right corner. And so on. In some cases Thom considered intentional certain alignments that are in fact lacking any common archaeological context, inventing connections between, for example, standing stones of the Neolithic Age and tumuli of the Bronze Age.
The critical revision of Thom's work certainly casts serious doubts on many of his extreme ideas, such as his conviction that megalithic man used a calendar divided into eight seasons that survived, in modified form, to this day, filtered through the Celtic calendar (this included the feasts Beltane, around May 5, today's May Day; Lammas, early August, today's Feast of the Assumption; Samahin, early November, today's All Souls' Day; and Imbolc, early February, today's Candelmass). The widespread and accurate use of the same unit is challenged as well, together with the precision of many alignments. What concerns us most here, however, is the fact that the technical criticisms of Thom's work may have profound consequences for anyone attempting to base even a part of the study of ancient thought on archaeoastronomy, for to dismiss the observation of the skies in megalithic times as a matter of ""purely symbolic interest'' entails negating the possibility of an astronomical thought, which in turn dismisses any scholarly insight, via archaeoastronomy, about the megalithic thought as a whole. Thus, although I agree with most of the technical critics, I tend to disagree with the ""reductionist'' position they might imply.
First of all, the equation "low precision = symbolic knowledge'' is somewhat misleading. There is, indeed, no absolute definition of precision. A clock that loses two minutes per year is very precise with respect to our daily requirements, but terribly imprecise if it is being used to program a Space Shuttle mission. Any definition of precision must be conditioned upon the purpose for which the measurement is made. The sun, for example, is very close to the solstice point for a period of several days, which could have led people to believe that the inversion of the movement of the sun's rising point at the horizon was predicted for a certain day, without necessarily knowing whether the exact day had been predicted or not. Even if the degree of precision in such a case is not high by modern instrumental standards, it was precisely what was needed to establish the authority of those who made the predictions (see Chapter 15 for more on this point).
This preliminary observation aside, we then have the strictly technical problem of determining if the criticisms of Thom's research are applicable to all the monuments he studied. Indeed, as Mackie has pointed out—and I tend to be in agreement with him—it would be sufficient to provide a thorough demonstration (e.g., by including analyses not only of the astronomical aspects but of the complete archaeological context) of the existence of just a single site in which Thom's "high criteria'' for precision had been met, and the "purely symbolic'' argument would have to be reconsidered, without taking anything away from the importance of the critical studies of Thom's results.
As an example, Mackie studied an isolated and rather unspectacular megalithic site, Kintraw, on the west coast of Scotland. Kintraw is home to a small tumulus and a single menhir. It is difficult to imagine Kintraw as a gathering place, as the site of rites and ceremonies, so there must be another reason why the megalithic builders chose it. Thom had discovered a curious phenomenon that allowed Kintraw to lend itself to extremely precise measurements of the sunset azimuth of the winter solstice, a phenomenon similar to the one we encountered at Maeshowe: the "double sunset.'' Seen from Kintraw, the sun sets behind a rocky pinnacle on the island of Jura, then rises again for a few moments after having passed behind the pinnacle, finally setting definitively at the horizon. The thing is, you cannot really see this from ground level; you have to climb the tumulus. How, one might ask, did they know where to build the tumulus? Well, on the other side of the complex, on the side of a hill, Thom had found a natural clearing with a half-buried boulder that, when he stood on it, allowed him to calculate the alignment with precision. To test the validity of Thom's results, Mackie studied Kintraw with the aim of establishing whether there was any archaeological proof that would confirm the significance of this particular alignment. Although he did not find any datable archaeological material, he did discover that the aforementioned boulder which had appeared to be natural was in fact a pair of hewn slabs configured like a V: the slabs had likely been placed there deliberately to mark the exact point from which to view the "double sunset'' of the winter solstice. In addition to Kintraw, Mackie also studied other sites, such as the lunar observatory of Ballinaby, where "precise'' measures are likely to have been performed (Mackie 1974; for discussion see Mackie 2002, Ruggles 1999, Ruggles and Barclay 2000).
New results on megalithic astronomy accumulate year after year, and though the debate on accuracy and megalithic science remains open, I think it has become impossible to deny the central role played by astronomical observations in the planning, construction, and use of megalithic monuments, so that Thom's work will always stand at the foundation of this important achievement. An especially significant example of astronomically related megalithic monuments that has been well studied in recent years is that of the so-called recumbent stone circles, which can be found by the dozens in northeastern Scotland. They are circles of stones, all standing except for one, which is laid horizontally on the ground between two vertical elements to form a sort of altar. This singular disposition gives the circle a main axis of symmetry, creating a resemblance to the megalithic "sanctuaries'' of the Balearic Islands, which we will discuss in the next chapter. As a rule, the axis of the recumbent stone circles is oriented west of south, and the archaeoastronomical studies of these monuments (Burl 1976, Ruggles 1984, Ruggles and Burl 1985) demonstrate beyond all doubt the interest of the builders in the azimuth of the southern major lunar standstill. The monuments were therefore used for rites that included observing the setting of the moon, which would have appeared to "sit'' upon the recumbent stone, framed by the flanking vertical members.
Together with the problems of interpretation goes the question of the date of the earliest expressions of astronomically based architecture, which is continually being pushed further back into the past as archaeologists steadily make new discoveries. The last one was in 2003 in Gosek, Germany, where aerial photography revealed what remains of a henge of wooden posts approximately 75 meters in diameter, with three openings aligned, respectively, with north and the sunrise and sunset azimuths of the winter solstice. Carbon-14 testing of remains from the site gave a date somewhere around 5000 BC.
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