A New Survey of Neolithic Dolmens in Central Portugal

Fabio SilvaSophia Centre for the Study of Cosmology in Culture, Department of Archaeology & Anthropology, University of Wales Lampeterfabpsilva@gmail.com

Published in Journal of Cosmology, 2010, Vol 9, 3094-3106

Abstract Megalithism has been associated with prehistoric astronomy in Europe for quite some time

now. Various comprehensive surveys of these monuments suggest that they are oriented not

randomly but to particular areas of the horizon where astronomical events, such as sunrise or

moonrise could be witnessed and even predicted. In Portugal, an area which has been

overlooked by researchers, that of central Portugal, is actually the second densest region of

megalithic monuments in the country. A comprehensive survey of the orientation of Iberian tombs

made by Hoskin and colleagues included the measurements of orientation of the axis of some

tombs in this region. He concluded that most tombs in the Mondego plateau were aligned

towards sunrise during the winter seasons, whereas for other nearby river basins dolmens were

categorized as aligned with sunrise/sunclimb. The archaeological evidence that has come to light,

suggested to archaeologists that the megalith builders’ way of life as semi-nomad pastoralists

was tied to the orientation of the dolmens, namely that the monuments were built during the

winter seasons when the pastoralists would be in lower ground.

However not all measured dolmens fit this picture. To test this seasonal model a new

survey was planned and conducted during the spring of 2010, which tried to be more attentive to

landscape features and other possible orientations as well as incorporating previously

unmeasured tombs from the region. The employed methodology and subsequent results are

presented. The survey confirms Hoskin’s results but not their interpretation. The case for a new

way to fit megalithism into the seasonal economic model of the Neolithic communities is argued

for based on the gathered data. Some of the surveyed tombs suggest a non-solar alignment,

possibly lunar or even stellar. A couple of Mondego dolmens forming one of the oldest Neolithic

necropoleis of the region have their entrances towards the northern sky, which might indicate an

early stellar association with death and the afterlife.

Key Words: archaeoastronomy, anthropology, neolithic, alignments, Portugal

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A New Survey of Neolithic Dolmens in Central Portugal

Fabio Silva

1. Megalithism and Prehistoric Astronomy The general phenomenon of megalithism in Europe is a very old one in archaeology.

These monuments, built with massive stones sometimes weighing more than 50 tons, appear all

over Atlantic Europe (see Fig.1).

Figure 1 - The distribution of Neolithic tombs in Western Europe indicating what Renfrew believes to be

regions where these monuments developed independently. Adapted from Renfrew (1999, p.139).

According to Vítor Oliveira Jorge (1987) the understanding of european megalithism only

truly set off after dendrochronology was used to calibrate radiocarbon dates. Colin Renfrew

(1999), based on the new dates, introduced two fundamental aspects to the study of prehistoric

europe: first, that the megaliths were independent creations of Neolithic peoples of the European

Atlantic coast; and second, he tried to explain its origins in palaeo-sociological and demographic

terms, thus suggesting that the similitudes between european megaliths were due to similar social

conditions (Jorge 1987, p.219). Renfrew proposed that the farmers belonging to the Neolithic

culture, advancing from the Middle East, as genetic analysis suggests (Cavalli-Sforza 2001), upon

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reaching the expansion barrier that is the Atlantic coast, would have developed a particular sense

of territory. The megaliths would be erected to mark those territories.

More recently however, with more data from the Mesolithic, archaeologists are beginning

to see the Neolithic, at least the Early Neolithic, as a continuation of the Mesolithic, as opposed to

a cultural invasion by Middle-Eastern farmers (Tilley 1994). Tilley argues that Neolithic monuments

were built in places that were already important and being used by Mesolithic populations as

‘ceremonial meeting-points on paths of movement’ (Tilley 1994, p.109). He also suggests that

their purpose, or at least, one of them, was to draw attention to natural markers in the landscape.

These markers would probably have a symbolic, social significance, much like the natural markers

in Aboriginal Australia’s walkabouts.

Another hypothesis is that these monuments marked astronomical events. In fact some

view the celestial sphere as a natural extension of the landscape, and thus archaeoastronomy as

a tool complementary to landscape phenomenology (Sims 2009). Neolithic cultures had no written

language, which means that there are no written records of their beliefs, their cosmology. One can

only infer them from what they have left behind, namely the megaliths themselves, occupation

sites, and other archaeological artifacts. Archaeoastronomy helps by discerning whether

astronomical objects like the sun, moon or stars, or events, like full moon or summer solstice,

held any significance for the megalith builders.

As an example, Ruggles (1999) did a massive survey of over 300 megalithic monuments of

various kinds in the British Isles. His results show a preference for alignments with lunar standstill.

Such an enormous amount of monuments oriented towards a single event, especially one that

only occurs every 18.6 years, must mean that it had some special significance for the people who

built them. It probably involved a massive gathering at the monuments and ensuing rituals (Sims

2006; Sims 2009). According to Sims (2006), that the lunar standstill was an important ritualistic

event comes naturally out of a transition, a counter-revolution, from an egalitarian, female-

centred, moon-based Palaeolithic hunter-gatherer cosmology (Knight 1995; Marshack 1991) to a

hierarchical, patriarchal solar cosmology characteristic of Neolithic pastoralists and farmers.

A massive survey of around 2500 megaliths in Southern Europe has been done by Michael

Hoskin (2001) with help from various colleagues. They found that most megalithic monuments

have an orientation due East, or between the Summer Solstice sunrise and the Winter Solstice

sunrise azimuths, although there are outliers. They concluded that the sun was at the centre of

megalithic cosmology in Mediterranean Europe, with a few punctual exceptions.

This paper’s focus is on a particular group of megaliths, the dolmens, or antas (in the

original portuguese) of central Portugal. These monuments are very simple in their architecture:

they have a central polygonal chamber, made out of megalithic orthostats, typically 5 or 7, which

is where the bodies and other votive offerings were laid. The chamber might then have an

entrance with or without a corridor, also built with orthostats. Both the chamber and the corridor

were covered with covering stones and the whole construction covered by a mound of earth and/

or stones, the tumulus or cairn. At its prime, a typical dolmen would look like an artificial mound,

with a single opening (see Fig.2).

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Figure 2 - Dolmen da Orca, also known as Orca dos Fiais da Telha (ref.no.27). A massive and well-

preserved dolmen of the Late Neolithic that preserves most of his tumulus.

In order to infer the cosmology associated with these megaliths it is essential to

understand what the archaeological records tell us about their builders, and how astronomy could

fit in their lives, which is explored in section 2. In section 3 the data gathered in a new survey of

dolmens in central Portugal is presented and discussed. It is argued that the naive association

between megalithism, astronomy and Neolithic seasonal economy put forward by previous

authors needs to be reviewed in light of the evidence. Future avenues of research are considered

in section 4. For the more avid readers appendix A includes all the methodological details of the

survey and appendix B all the raw data gathered.

2. The Megaliths of the Mondego platform and their Builders The region of central Portugal is the second densest in the country in megalithic

monuments dating back to the Neolithic. The Mondego platform, located in central Portugal (see

Fig. 3) is bordered by the Central Massif to the southeast, the Marginal Massif to the west and

northwest, and the Douro basin to the north. The area covers most of the drainage basins of the

upper Mondego, the Vouga and part of the Douro rivers. The Central Massif, especially the Serra

da Estrela, offers good pastures during the spring and summer seasons and has evidence of

human usage since the fifth millennium BCE. The archaeological record has allowed

archaeologists to come up with a model for the life of local communities during the Neolithic

which is presented next.

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Figure 3 - Map of Portugal, with distribution of megalithic monuments. The ellipse marks the area

under study, the second densest after Alto Alentejo. Adapted from Pereira (2004, p.64).

2.1 The Early Neolithic

Discoveries of the past twenty years, especially of occupation sites in the Mondego basin,

have allowed a clear picture of local life during the fifth millennium BCE, the Early Neolithic, to

emerge (Senna-Martinez and Ventura 2008a, pp.318-9). Small communities sustained themselves

by small game hunting, the gathering of acorn and other winter fruits, and transhumant

pastoralism. The raising of ovicaprids - sheep and goat, introduced to the region by the first

Neolithic settlers - suggests that spring and summer were spent on high ground pastures and

winter on lower ground (Senna-Martinez et al 1997, p.664). According to Senna-Martinez and

Ventura, later developments can be interpreted as the consolidation and intensification of this

seasonal form of economy. Pottery fragments attributed to this period show characteristics

belonging to the traditions of the Early Neolithic from Estremadura, to the southwest, and

Andalusia, to the southeast, allowing for the possibility of a dual origin (Senna-Martinez and

Ventura 2008b, p.80).

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2.2 The Middle Neolithic

The first megaliths were built at the turn of the Middle Neolithic, around 4000BCE, roughly

a thousand years after the first Neolithic communities showed up in the region (Senna-Martinez

and Ventura 2008a, pp.317-50). This first phase is characterized by monuments with a small

polygonal chamber and a short corridor or none at all. Some tumuli have complex structures in

front of them, including atria (see Fig. 4). These structures have been interpreted as ‘scenic

spaces’, with the monuments being used as temples, with closed, possibly reserved, spaces (the

chamber and corridor) and open spaces for the general audience (the frontal atrium). Also, in

some dolmens one finds the first instances of megalithic art in the region. Artifactual evidence

associated with the burials are of the same kind as that found in early tombs of neighbouring

groups, namely Évora/Reguengos/Montemor in Alentejo, Serra da Aboboreira, Galicia in northern

Spain, and Estremadura (Senna-Martinez et al. 1997, p.662).

These monuments can be seen as ‘true anchors in the landscape for populations that, on

the other hand, have a high seasonal mobility’ (Senna-Martinez and Ventura 2008b, p.82). In this

way Senna-Martinez and colleagues fit the monuments into their economic model: the

necropoleis, by marking the territory, would legitimize their winter occupation.

Figure 4 - Plan layout of Dolmen 2 de Chão Redondo (ref.no.9). The chamber is located in A and the

corridor in B. Scenic structures C, the intratumular corridor, and D, the atrium are also shown. Adapted from

Santos et al. (2001, p.26).

2.3 The Late Neolithic

In the middle of the fourth millennium BCE there was a cultural shift that affected megalith

building in the region. This is now understood as the transition to the Late Neolithic (Senna-

Martinez and Ventura 2008a, p.333). Megaliths belonging to this phase are generally bigger and

possess developed corridors with heights that are different to those of the chambers, now usually

composed of 7 or 9 orthostats, and include intratumular corridors and frontal atria (see Fig. 4 and

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Fig. 5). This phase is also characterized by complete abandonment of smaller monuments from

the previous phase. Big monuments within a necropolis are rare in this phase, as they tend to

show up in isolation. The funerary deposits recovered from these sites also show an increase in

complexity of the funerary rites, with new elements having been introduced, like arrowheads.

Occupation sites in the Mondego basin appear in close proximity to the necropoleis and

suggest an autumn and winter occupation, as evidenced by the presence of central hearths and

earth ovens to roast and keep acorn. This is interpreted by Senna-Martinez and colleagues as

further evidence that these sites were being used as part of the seasonal model they proposed.

Figure 5 - Frontal atrium of Picoto do vasco (ref.no.6).

2.4 Megalithic Astronomy

During Hoskin’s survey of Mediterranean tombs, twenty-one dolmens in the Mondego

basin and a further twenty-two in adjacent river basins were surveyed between 1994 and 1997

(Hoskin 2001, pp.104-6). The orientation of the dolmen’s axis, that is, the orientation of the

entrance or corridor was measured. The tombs on the Mondego basin were classified as oriented

to the sunrise, even though there are a few outliers. Tombs in the adjacent Vouga, Paiva, Torto and

Coa basins were classified as oriented towards the sunrise/sun-climb.

This has been interpreted as a evidence for a solar-based cosmology, focused on the

darker months. Senna-Martinez et al. (1997, p.669), assuming that the orientation of the tombs

was chosen at the time of their building, claimed that the results are consistent with the

mentioned seasonal economic model. Most of the dolmens were found to be oriented towards

negative declinations, which, given the assumption, would indicate that they were built during the

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autumn or winter seasons, when the pastoralists would be in lower ground. Also, the only known

megalithic alignment in Beira Alta seems to be aligned with sunrise at winter solstice (Senna-

Martinez et al. 1997, p.669).

However, there are many problems fitting this model to the entire dataset. First of all, only

Mondego basin monuments seem to prefer negative declinations. The set of orientations of

monuments in other river basins show no such preference and, roughly, half of these monuments

have positive declinations. Also, two of the huts in a winter occupation site have their openings

towards the north-east (Senna-Martinez et al. 1997, p.670), indicating a possible positive

declination, and hence a summer sunrise, even though one can’t be sure without the horizon

altitude.

To explore these issues, thirty one dolmens in the area were surveyed in March and April of

2010, of which eleven had’t been previously measured by Hoskin’s team. All measurements were

made using a compass, clinometer and a GPS unit. For those interested, a discussion on the

employed methodology in included in appendix A, including the reasons behind the choice of

using a compass, the inherent dangers of doing so, and how to work around them. The raw data

for all the surveyed sites can be found in appendix B.

3. The Data and its Implications

Figure 6 - Plot of the declination of all data gathered during the Spring 2010 survey in central Portugal. See

main text for more details.

In Fig. 6 the declination of all measurements have been plotted. The figure includes the

axial orientations, represented as coloured dots, the windows of degeneracy (see section A.2),

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plotted as error bars, and other measured orientations represented by crosses (see table 2,

appendix B). The open circles around the dots represent measurements of sites where horizon

visibility was reduced, and thus have an uncertainty of a couple of degrees. The red and pink

horizontal lines mark the declinations for solstices and lunar standstills respectively, calculated for

the time period and region under study using Starry Night planetarium software. Twenty of the

dolmens surveyed had already been surveyed by Hoskin (2001), and his measurements are

represented by the diamonds in Fig. 6. There are differences in the declination values between

Hoskin’s survey and this one. Most of the new values are within 3º of Hoskin’s, which might

indicate a small systematic error or simply due to the problem of precision, as discussed in

appendix A.1

3.1 Testing the seasonal economic model

One can combine the two data sets and plot all the declinations for each river basin. This

has been done in Fig. 7 below. Dolmens with reference number higher than 31 were surveyed by

Hoskin only and they are indexed in the order they appear in the literature.

Looking at the figure it is clear that dolmens in the Mondego river basin do have a

preference for negative declinations. This, as mentioned before, fits nicely into the economic

picture of the Neolithic communities as described in section 2.

Figure 7 - Plots of the declinations of this survey (dots) combined with Hoskinʼs (diamonds), by river basin.

There are, however, four dolmens of the Mondego river that are oriented towards positive

declinations. Of these, ref.no.28 is discussed below, while the other declinations, those of ref.no.

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25 and 32, 33 (of Hoskin’s dataset: Lapa da Recainha and Dolmen de S. Pedro Dias), if they are

meant to be aligned with a sunrise, can be observed respectively nine, thirty-seven and twenty-six

days before or after an equinox. These can still fit the same seasonal framework, by noting that

equinoxes are not very obvious events in horizon astronomy (Ruggles 1999, pp.150-1). It is

possible, then, that they were not observed as markers of time. Instead, Mondego basin

communities would have been more flexible, and this was probably tied to the weather: after a

very long winter, a community might have stayed in lower grounds well after the equinox, moving

up to Serra da Estrela only when it was warm enough.

For the Vouga and Paiva river dolmens, however, when both data sets are combined, it

seems that they are almost evenly distributed, that is to say, there doesn’t seem to be any

preference for either positive or negative declinations. Whereas for dolmens of the Torto and Coa

river basins there seems to be a preference for positive declinations, but the samples are too

small for one to be able to say anything about them. The data is therefore calling for one of two

possibilities: i) either the economic model proposed by Senna-Martinez and colleagues applies

only to Mondego communities or ii) megalithism doesn’t fit the economic model in such a naive

way.

In favour of the first possibility, there is the fact that no occupation sites have yet been

found in river basins other than the Mondego and so there is no precise picture of Neolithic life in

those areas. The dolmens are themselves small and could have been built by small communities

that could very well have independent existences, with different ways of life and/or ideologies. It is

true that funerary artifactual remains are of the same kind as the ones found in Mondego tombs,

but this shouldn’t come as a surprise as they are also similar to the ones found as far south as

Alentejo as as north as Galicia, even though life in the plains of Alentejo, for example, had to have

been different. There are also small but significant architectural difference between dolmens in the

different river basins, especially between the Vouga and Mondego rivers (Ventura 2010, personal

communication).

The second possibility is, perhaps, much more tenable. This is to say that megalithic

ideology is much more complex than previously assumed. For instance, the megaliths in the

Vouga, Paiva, Torto and Coa basins are on higher elevations than the ones in the Mondego, this

would go against a possible construction during winter, which is the lower ground season. Also, in

this respect, as mentioned above, two of the habitation huts are oriented towards north-eastern

azimuths. If the same logic that was applied to the megaliths was applied to them a paradox

between the evidence for winter use (the hearths and earth ovens) and the orientation towards

summer sunrises emerges. A new model would then be needed, and such a model would need to

explain all the data, including why Mondego basin monuments prefer negative declinations. A few

of the outliers identified by this survey suggest alternatives.

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3.2 Outliers and alternatives

The Orca de Pendilhe (ref.no.5) has a very low declination, lower than both the sunrise or

moonrise lower extremes. This is most likely due to the fact that this tomb’s corridor was

reconstructed (Cruz 2000, p.35), whereas the orientation of a line parallel to the two surviving

original corridor orthostats gave a very different declination (the cross of ref.no.5 in Fig. 6), well

within the lower limit for the southern major lunar standstill. Thus, this dolmen suggests a

moonrise alignment, possibly to a southern major standstill limit.

Another particularly interesting outlier is the Ameal necropolis in Carregal do Sal,

composed of two Middle Neolithic dolmens, Orca 1 (ref.no.28) and Orca 2 (ref.no.29), separated

by a mere seventy-five metres (Pinto and Senna-Martinez 2006, pp.51-2). The former’s opening is

oriented towards a very high positive declination, higher than the summer solstice and northern

major lunar standstill declinations, and this is also one of the possibilities for the second dolmen,

whose badly damaged state made it difficult to discern which one was the original entrance (all

three hypothesis are marked by crosses in Fig. 6, two of which are almost superimposed) (Ventura

1998, pp.30-51). It is therefore a possibility that this very early necropolis was oriented towards

the northern sky. This might indicate a circumpolar star based ideology, most likely associated

with death (the dolmens were, after all, tombs), not dissimilar to what is found in the Egyptian

Predynastic and Early Dynastic (Malville et al. 2007; Lehner 1997, p.33; Belmonte 2001). If this is

true, the local Middle to Late Neolithic transition would have entailed a cosmological

transformation not unlike Sims’ counter-revolution in the British Neolithic (Sims 2006), but starting

from a star-based cosmology. There is evidence of such a stellar to solar transformation in the

early periods of Ancient Egypt as well (Hart 2005, p.153).

4. Concluding Remarks & Future Work In this paper it was argued for a reinterpretation of the data concerning alignments of

megalithic dolmens in central Portugal and beyond. In his conclusion, Hoskin extends Senna-

Martinez and colleagues’s assumption that the corridor and entrances to the tombs were ‘laid out

to face sunrise on the day that construction began‘ (2001, p.213) to the whole of the Iberian

Peninsula. Such a view considers all the outliers as anomalies. There is however a different way to

approach the dataset, and that is not to disregard the outliers which should also be explained by

the model. Some of the stones in these tombs required more than 30 people just to move them,

and the average amount of time to build a Late Neolithic dolmen exceeds the 880 hours of work

(Senna-Martinez and Ventura 2008a, p.337), that is more than a month if nothing else was being

done, but most likely two to three months of labour. It is very difficult to accept the builders

wouldn’t notice if they had done a mistake, that they wouldn’t stop working or readjust a tomb

that wasn’t aligned to the right astronomical event.

In this sense, the entire dataset for central Portugal, which includes many monuments

oriented to positive declinations, is evidence that a new model, a new way to tie-in megalithism

with the Neolithic lifestyle and thus infer their ideology, is needed. Discovery of occupation sites in

the Vouga and Paiva regions would help get a better archaeological picture of these regions.

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Statistical analysis might also shed some light on this fact, and it would be interesting to see

whether the dolmens in these basins are statistically distant from the Mondego ones in the

approach taken by González García and Belmonte (2010), indicating the possibility of differing

groups, and possibly ideologies, in the area.

Some of the tombs suggest a lunar or even stellar alignment. The possibility for alignments

not with sunrise, but with moonrise is also not discounted by the dataset. This would be in line

with previous findings in the British Isles (Sims 2006; Ruggles 1999). The Ameal necropolis, dating

to the Middle Neolithic and therefore one of the earliest, suggests a northern sky alignment. There

is another dolmen dated to the same period and near Ameal, Orca 2 de Oliveira do Conde and

although it was found in a badly damaged state, it might still be possible to measure the

orientation of its entrance (Pinto 2005, pp.52-3). There is also at least one other dolmen close-by,

Cabritos 2 in the north bank of the Douro basin, surveyed by Hoskin, that also has a high positive

declination of 47º (Hoskin 2001, pp.106-7), practically the same as Orca 1 do Ameal (ref.no.28)

and that might be worth visiting. These possibilities will be the focus of a second stage of the

survey.

Acknowledgements The author would like to thank the, too numerous to name, local councils and museums

that were helpful not only in allowing the measurements to be made but also in providing

documentation on the sites, as well as all those that accompanied him during the survey, and

those that read and commented on this manuscript.

This work was done while the author was being supported by FCT (Portugal) fellowship

no. SFRH/BD/27249/2006.

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AppendicesA. Methodology The dolmens of central Portugal were covered by a tumulus or cairn, always round or

slightly ellipsoidal, with a single opening where the corridor (and other scenic spaces, if present)

lies. The very circular symmetry of these monuments, their simplicity when compared to British,

Irish or French monuments of the same period, the lack of contemporary archaeological remains

outside the chamber and scenic spaces, and the paintings within the chamber, and in some cases

the corridor as well, suggests that the only meaningful axis was the corridor/entrance axis. The

key measurement to take was then the orientation of this axis. All measurements were made

using a compass, clinometer and a GPS unit. In this appendix, the employed methodology is

explained.

A.1 The Problem of Precision

Even when a long corridor has survived intact, or been accurately restored, the

determination of it’s orientation is plagued by difficulties. The inherent non-uniformity of the

orthostats used, as well as irregularities in their laying, might mean that their builders either were

limited by technology, or that a perfect alignment of the corridor walls simply wasn’t important to

them. In either case approximations have to be done on the field to determine the central axis of

the tomb. This means that slightly different techniques will give azimuth values that can differ by

as much as two to three degrees (Hoskin 2001, pp.11-2). Under such conditions, measuring to an

accuracy of arc-minutes, as can be achieved by using a theodolite, seems superfluous as the

instrument’s accuracy won’t translate into orientation accuracy.

Whenever a corridor was present the axis was determined by halving the lengths of it’s

openings, placing a surveyor’s rod on each and taking care for them to be as vertical as possible

(see Fig. A1). They were then used as foresights to measure the azimuth, az0, with the compass.

For Middle Neolithic tombs, however, or where the corridor didn’t survive, a yet greater

approximation was taken by halving the length of the chamber entrance, and using the centre of

the backstone as a second foresight.

Figure A1 - Plan layout of Orca da Malhada do Cambarinho (ref.no.1). The dotted lines were measured,

their half-length determined on-site and a surveyorʼs rod placed on these points. These were then used to

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determine the axial direction az0. The “window” azimuths azN and azS were determined by using a

surveyorʼs tape to extend the diagonals of the corridor further afield. Surveyorʼs rods were then fixed in these

directions and used as foresight. Adapted from Marques (2005, p.44).

A.2 Degeneracy in Orientation

However, one shouldn’t assume that our Western notions of axis, orthogonality, or even of

corridor and line, were popular six thousand years ago. In fact, megalithic art seems to prefer

curvilinear motifs to straight lines (Jorge 1998; Lewis-Williams and Pearce, 2009; Power 2004).

Therefore even though, from one’s modern understanding, the corridor is precisely oriented, the

intention of its builders might have been a different one. It is possible that the corridor was only

meant to indicate a general direction, and a feature of the landscape would indicate the precise

point of the alignment. Another alternative is that light, from sun, moon or star, was meant to

shine within the chamber, but not necessarily on the backstone. We then have a range of possible

axes that, if looking only to the corridor or chamber entrance, one cannot say which ones are

meaningful. This is akin to the concept of degeneracy in quantum mechanics, where one cannot

distinguish between two quantum states with the same energy level. To distinguish them one has

to measure other quantities, much like in this case where one needs to take into account the

horizon landscape and the presence, or likelihood of presence, of drawings or engravings within

the chamber’s orthostats.

This inherent degeneracy in the exact orientation can be accounted for by measuring the

window of visibility to the horizon, from the chamber, that each corridor permits. In this way one

measures a maximum azimuth range that includes all the horizon points at which light from a

rising astronomical object would shine within the chamber. This is, of course, a one dimensional

measure of said degeneracy. A more complete measurement would have to include the height of

the corridor and chamber entrances, that is, the maximum altitude that the sun, moon or star

could be so that its light would shine within the chamber’s orthostats. However, most of the

surveyed tombs have no surviving corridor cover-stones so such a measurement is an

approximation at most, but this should be considered in the future.

This was achieved by using a steel surveyor’s tape to determine the diagonals of the

corridor, that is, the maximum lines of visibility that the first and last sets of corridor orthostats

permit from within the chamber. Surveyor’s rods were then placed along these lines and their

azimuths taken (see Fig. A1 and Fig. A2). In the appendix these measurements have been labeled

azN and azS, meaning the azimuth, respectively, north and south of the axial azimuth az0. This

means that the northernmost horizon position (lowest azimuth) that, for e.g., sunlight can shine

within the chamber is azN, illuminating the right side of the chamber. The other extreme position,

azS, is the southernmost rise position for light to shine, this time, on the left side of the chamber.

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Figure A2 - Measuring the degeneracy window at Orca da Malhada do Cambarinho (ref.no.1).

Measuring such a range while in the field, also allows one to focus attention on that

particular region of the horizon when looking for features that might have been used as foresights,

or simply just markers, for astronomical risings (see Fig.A3).

Figure A3 - The corridor of Dolmen da Lapa de Meruje (ref.no.2) is aligned with a particular stone in the

local horizon, which might have served as a foresight for an astronomical rising.

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A.3 Magnetic Deviations

Using a compass on the field, even when it makes more sense to use one than a

theodolite, is still problematic due to local magnetic deviations (Ruggles 1999, p.165). These

include local magnetic anomalies, due to ferromagnetic material in the vicinity, and the magnetic

declination, that is the difference between magnetic north and true north.

Local magnetic anomalies are relatively easy to minimize. One needs only to measure

azimuths in both directions so that later one can take the average of the two measurements.

During the survey this was done for all measurements of horizon azimuths.

The magnetic declination, however, varies from place to place, and from time to time, and

even though it is relatively easy to find it in military or other detailed maps, or even estimated

values on the web (via NOAA’s Geophysical Data Center), there are nagging uncertainties involved

in both, and it is always better to measure it on the field.

One way to do this is to use a combination of compass and GPS measurements. By taking

measurements of azimuths of visible landmarks whose coordinates can then be measured with

the GPS unit, one can calculate their true azimuth and compare it with the magnetic one. If this is

done for multiple landmarks, lying radially from the dolmen, one can take the average of the

magnetic deviations.

This technique proved to be very exact, always giving a magnetic declination that was, at

most, within a degree of the estimated value obtained from NOAA’s website. For six or seven

measurements this comes down to 0.6º, with an error of only 0.4º for at least one site (ref.no.1).

Note, however, that backsighting was not done for these measurements, but one would expect

that the resulting values would be further improved by this.

16

B. Corpus Mensurarum - Spring 2010 Survey Data

Table 1 - List of surveyed sites, with reference number, CNS national catalogue number, location, GPS coordinates and elevation ( * denotes sites where the elevation was obtained using Google Earth software, all other were measured on-site using GPS).

Ref.No.

CNS Name Location GPS Lat. GPS Long. Elev.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

13940 Orca da Malhada do Cambarinho Viseu/Vouzela/Ventosa 40º40’47.8”N 8º7’13.8”W 811

13913 Dolmen da Lapa de Meruje Viseu/Vouzela/Carvalhal de Vermilhas 40º38’27.4”N 8º8’21.8”W *924

7498 Dolmen da Arca Viseu/Oliveira de Frades/Arca 40º36’27.6”N 8º12’48.8”W 672

308 Juncais Viseu/Vila Nova de Paiva/Queiriga 40º48’57.9”N 7º43’50.6”W 762

2232 Orca de Pendilhe Viseu/Vila Nova de Paiva/Pendilhe 40º53’53.3”N 7º49’25.3”W 818

Picoto do Vasco Viseu/Vila Nova de Paiva 40º54’05.8”N 7º48’32.3”W 885

1341 Castonairas Viseu/Vila Nova de Paiva/Fráguas 40º50’05.3"N 7º45’19.8"W 722

11769 Merouços Viseu/Vila Nova de Paiva/Touro 40º55’14.6"N 7º43’18.1"W 904

12500 Dolmén 2 do Chão do Redondo Aveiro/Sever do Vouga/Talhadas 40º39’50.7”N 8º18’42.7”W *474

12505 Anta de Capela de Mouros Aveiro/Sever do Vouga/Talhadas 40º41’29.3”N 8º18’14.4”W 611

1463 Dolmen da Cerqueira 1 Aveiro/Sever do Vouga/Couto de Esteves 40º46’48.1”N 8º18’35”W 529

750 Dolmen 1 do Carapito Guarda/Aguiar da Beira/Pena Verde 40º44’48.4”N 7º28’0.7”W 651

2091 Anta de Cortiçô Guarda/Fornos de Algodres/Cortiçô 40º40’14.7”N 7º30’19.2”W 701

751 Dolmen da Matança Guarda/Fornos de Algodres/Matança 40º40’08.2”N 7º31’57.4”W 618

1395 Anta da Cunha Baixa Viseu/Mangualde/Cunha Baixa 40º34’12.2”N 7º46’15.3”W 411

11615 Anta da Orca Guarda/Gouveia/Rio Torto 40º30’1.3”N 7º39’17.4”W 454

460 Anta de Pêra do Moço Guarda/Guarda/Pêra do Moço 40º37’34.9”N 7º11’51.1”W 792

7316 Lameira de Cima 1 Viseu/Penedono/Ourozinho 40º56’9.9”N 7º20’57.5”W 906

7322 Lameira de Cima 2 Viseu/Penedono/Ourozinho 40º56’10.7”N 7º20’57.9”W 909

7382 Dolmen do Carvalhal Viseu/Penedono/Penela da Beira 41º1’25.3”N 7º26’30.1”W 908

891 Dólmen-Capela de Nossa Srª do Monte Viseu/Penedono/Penela da Beira 41º1’24.1”N 7º26’29.5”W 911

7384 Dolmen de Sangrino Viseu/Penedono/Penela da Beira 41º1’0.3”N 7º26’41.9”W 889

2850 Orca das Pramelas Viseu/Nelas/Canas de Senhorim 40º30’46.5”N 7º54’47.7”W 382

7024 Orca de Santo Tisco Viseu/Carregal do Sal/Oliveira do Conde 40º27’32.4”N 8º0’18.6”W 316

2826 Orca do Outeiro do Rato Viseu/Carregal do Sal/Oliveira do Conde 40º27’47.3”N 7º55’28.1”W 339

Orca do Santo Viseu/Carregal do Sal 40º27’1.3”N 7º56’2.5”W 332

2825 Dólmen da Orca Viseu/Carregal do Sal 40º26’37.9”N 7º56’17.3”W 325

2824 Orca 1 do Ameal Viseu/Carregal do Sal/Oliveira do Conde 40º26’32.9”N 7º56’37.2”W 339

7054 Orca 2 do Ameal Viseu/Carregal do Sal/Oliveira do Conde 40º26’28.7”N 7º56’38.6”W 329

18015 Orca da Palheira Viseu/Carregal do Sal/Oliveira do Conde 40º26’38.6”N 7º57’1.3”W 297

4018 Dólmen de Antelas Viseu/Oliveira de Frades/Pinheiro 40º42’45.2”N 8º14’38.1”W 513

17

Table 2 - Data collected at the sites, including: phase (LN for Late Neolithic, MN for Middle Neolithic, “?” denotes uncertainty in attribution due to lack of literature on the sites), average azimuth along the axial direction az0, altitude along the same direction alt0, window azimuths, azN and azS, and horizon altitudes, altN and altS, as well as other measured orientations or alignments.

Ref.No.

Pha. az0 alt0 azN altN azS altS Other orientations

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

28

29

30

31

LN? 114.75 4.5 105.25 5.5 125.25 4.5

LN? 91.5 9 79.75 10 95 8 Perpendicular to the entrance: az=105.5, alt=7 (altrock=5), Perpendicular to main orthostat: az=96, alt=8.5

MN? 80.75 4.5 Perpendicular to the main orthostat: az=48.75, Bearing to a strangely shaped orthostat in the surroundings: az=156.5

LN 79 3 72.25 2.5 86.75 4

LN 148.5 3 Parallel to single corridor orthostat: az=129, alt=2.5

LN 113.25 0.5 101.5 0 119.75 0.5

LN 110.25 6.5 92.75 5 128.25 9

LN ~90 2

LN 69.5 ~0 49.75 ~0-4 88.5 ~0-3

LN 102.5 3 94.25 ~2.5 117 ~2

LN? 73.75 ~0 62.5 2 92.25 3

MN Rock in the horizon: az=94, alt=4.5

LN 122.25 2 110.25 3 133.5 2

LN 100.5 3.5

LN 112.25 3 104 3 -4 124.25 3 -5

LN 112.25 6 78.25 4 150.5 7

LN 89.5 6.5 64 3.5 113.25 8.5

LN 90.25 0.5 92 0 99.5 0

LN 84.25 0 79 0 104.75 0.5

LN? 70 4.5 44.5 4 101.25 3 Parallel to corridor walls: az1=84, alt1=4; az2=61, alt2=4

LN? 90.5 4 72 4.5 108.75 3 Parallel to corridor walls: az1=98, alt1=3; az2=86, alt2=3.5

LN 92.75 4.5 Parallel to intratumular corridor walls: az1=123.25, alt1=3; Mound in the horizon: azm=117, altm=4

LN? 111.5 ~3

LN 121 4 96 4 144.5 5

LN 88.25 ~4 74.75 4 105 3 Parallel to outside part of corridor: az2=98.75, alt2=3; Diagonals of outside part of corridor: az2N=77.25, alt2N=4; az2S=127.25, alt2S=5; Direction of stone in chamber entrance: azp=82, altp=5

~102 3

LN 112.75 2.5 101.5 3 120.5 3 -3.5

MN 21.5 4 5 3 h=24.5,d=1.30m

MN 123 3-3.5 Other possible entrances: az1=356, alt1=4; az2=0, alt2=4

LN? 97 5

LN 93.5 -2-3

18

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