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Samhain dawn sunbeam penetrating to backstone in Cairn L, Carrowkeel Martin Byrne

The Mound of Óengus (Newgrange),
3700 - 3200 BCE

Entrance to Newgrange

Sunbeam entering Newgrange
Dawn, Winter Solstice

The chamber at Newgrange

Path of sunbeam at Newgrange

Illuminated backstone, Dawn, Spring Equinox Cairn T, Loughcrew

Calendar petroglyphs
Backstone, Cairn T, Loughcrew

"We have already destroyed an estimated 60 percent of the archaeological monuments in Cork, 44 percent in Kerry, 40 percent in Antrim, 31 percent in Tipperary and 29 percent in Donegal. At this rate there will be very few possible astronomical alignments left to argue a war of ideas."
   – Martin Brennan


Ireland is well known for her literature and music, but less so for the thousands of ancient megalithic sacred sites which are perhaps her greatest treasure. These include standing stone circles, raths, dolmens, cairns, barrows and passage mounds, some of which are over 100m in diameter, elaborately constructed with internal passages and chambers, featuring hundreds of decorated stones engraved with petroglyphs of astronomical significance.. Built of massive unhewn rocks and smaller stones and earth, they are often found on heather covered mountain tops and dramatic natural settings, with a wildness in their beauty like a falcon's nest. The most famous excavated site is the Boyne Valley complex in County Meath, described by UNESCO as "the largest and most important expression of prehistoric megalithic art in Europe". Named after the River-Goddess Bóann, this site includes the great chambered cairn of Óengus, the Love God, known in English as Newgrange, shown in the photographs at left, together with the cairns of Knowth and Dowth, and dozens of smaller satellite mounds and outlying standing stones. The great cairn at Newgrange measures 110m. in diameter, and contains a 19m. passage leading to a tall central corbelled chamber, thought to be the oldest roofed chamber in the world, and three side-recesses. At the moment of sunrise on the Winter Solstice, a beam of sunlight penetrates the cairn through the roof-box which is visible above the entrance in the photo on the left, reaching into the passage all the way to the middle of the chamber, past a triple-spiral petroglyph which matches the design of the giant kerbstone that lies before the entrance.

Astronomical alignments are also found at Loughcrew on Slieve na Caillaigh (the Mountain of the Sorceress) in Meath, Carrowmore in Sligo, and elsewhere. Other major cairn sites include Tara in Meath, Carrowkeel, Lough Corrib, the Wicklow mountains, and the great cairn of Queen Maeve on the summit of Knocknarea in Sligo overlooking the Atlantic ocean, perhaps the most important unexcavated Neolithic monument in Europe. See the photo gallery 1 for main pictures, and photo gallery 2 for views of Knowth.


These monuments were built in the Mesolithic and Neolithic periods (middle and late stone age) by pre-Celtic Indigenous People who inhabited Europe before the great Indo-European invasions of the bronze age. Irish mythology refers to the Irish group as the Tuatha Dé Danaan – the People of the Goddess Danu, and says that they built the monuments. Recent genetic research confirming the presence of a pre-Indo-European race in Ireland has emerged through the discovery that the DNA of many of the inhabitants of Connacht (Ireland's most remote and least developed province in the West of the country) contains genes that are shared by no other European people apart from the Basques, whose language and origin is widely recognised as being pre-Indo-European.

We also know that these People of the Goddess were avid watchers of the night skies, for they have left us with an archaeological legacy of tens of thousands of great stone artworks, which withstood the turbulence of history and adorn the Irish landscape to this very day. Many of these appear to be designed as multi-purpose ritual centres, tombs, and astronomical observatories.


The earliest Irish mythology contains no mention that the monuments were tombs, but refers to their various astronomical aspects. These are also mentioned in manuscripts from the 5th century onwards, and in recent centuries in reports by the military surveyor General Charles Vallancey published from 1782 to 1806,. in poetry by A.E. (George Russell) in 1897, in anthropology by W.Y. Evans-Wentz in 1909, in astronomy by Sir Norman Lockyer in 1909, in books by Alfred Watkins in 1925, by Alexander Thom and John Woods, by John Patrick in 1974, by the archaeologist M.J. O'Kelly in 1969 and 1982, by John Michell in 1989, by Tim O'Brien in 1992, and by the art historian Michael Dames in 1996. The most eloquent account was made by the artist Martin Brennan in his book The Stars and the Stones: Ancient Art and Astronomy in Ireland (Thames and Hudson, London, 1983).

As works of art or contexts of information, they focus the viewer's attention on man's place in the cosmos. The design of the chambered cairns involves the orientation of passages, the position of petroglyphs on decorated stones within the passages and chambers, the location of outlying stones that function as astronomical markers and also as sundials, and the motion of the sun, moon and stars. Most impressive is the projection of light beams cast into the darkened chambers by the sun and moon, which spotlight sequences of petroglyphs that appear to be symbols and records of the astronomical phenomena to which they are thus linked. The whole system permits the observation of the motion of the planets and the stars, and the prediction of the Equinoxes, Solstices, and the four Cross-Quarter Days, making it possible to celebrate gatherings and ritual events on these fixed dates which mark the cycle of the ancient European calendar.

Like the humble Chinese abacus which can perform surprisingly complex mathematical computations, these megalithic instruments yield rather more sophisticated results than a naïve observer might expect.

As instruments for the measurement of time, some of the cairns appear to have enabled their users to synchronise the lunar cycle with the solar one, thus creating one of the earliest accurate measurements of the solar year. Brennan is convinced they form "elaborate chronometers and calendars for the measurement of time and for the synchronisation of hunting, herding and agricultural activities to the ecological rhythm of the Earth's seasons, and to the longer cycles of astronomical epochs".

Petroglyph classification
by Martin Brennan


The hundreds of petroglyphs are certainly decorative, but research indicates that many of them have precise astronomical symbolic function. Evidence for this has been well argued by Martin Brennan.

Research on the meaning of the symbols requires careful observations in situ of the way their are illuminated in their intended context by the sun and moon throughout the year. This process is difficult and time-consuming, and is often hampered by cloudy skies. Of particular interest is the precise ways in which they become illuminated, or have shadows cast upon them by outlying gnomon stones, at moments of astronomical significance such as the two Solstices and Equinoxes, and the four cross-quarter days.

Boyne Valley astronomical alignments
(click map for to enlarge)


Apart from the astronomical orientation of the petroglyphs and passages, and the light beams which penetrate into the latter, the geographical position of the monuments upon the landscape often involves local alignments between larger monuments and their outlying satellites and standing stones, and long-distance alignments between monuments at remote locations. Major sites including Newgrange and Maeve's Cairn on Knocknarea are usually the focal point of these so-called ley lines which appear to criss-cross the landscape with uncanny precision, sometimes stretching for many miles across mountains and valleys beyond the horizon where no direct line of sight is possible. Many of these are astronomically aligned (including some 40 known and/or suspected alignments in the Brú na Bóinne complex alone), but the orientation of others is a mystery. Various hypotheses have been explored to explain it, including theories of dowsing and geomancy which hold that the Earth's magnetic field flows through channels like the bio-electric meridians used in acupuncture and oriental medicine.

Winter Solstice sunrise at Newgrange:
beam of light penetrating the passage

Aerial view of Newgrange


Ireland's megalithic legacy is a global treasure, and much astronomical, anthropological, mythological and other research is needed to comprehend the meaning of its art, its grounding in the land, its focus on the stars, and its relationship to time. Readers who are curious to understand the mythological and historical context of the monuments should read the brief historical background on a separate page.

The astronomical design of the monuments seems obvious to anyone who has studied the mythological references and observed the sunbeam which still enters the 40-meter Western passage at Knowth around sunset on the Spring and Autumn Equinox, the corresponding beam which may have entered the cairn's Eastern passage around sunrise on the same dates, or the 30-meter sunbeam which illuminates the darkness of Newgrange at dawn on the Winter Solstice, over five millennia after its construction, as broadcast live on television in 1999.

Martin Brennan's field observations led him to conclude that virtually all of the mounds in the Boyne Valley, plus those at Loughcrew and Tara are solar constructs. He was therefore outraged that "Twentieth century archaeological reconstruction [of the largest of the two passages at Dowth] has completely ignored any possible astronomical function, a modern artificial entrance has been built and the original entrance sealed like a tomb. A reconstruction that ignores the possible astronomical importance of a passage mound is no more nor less than an act of vandalism." As the journalist Anthony Murphy points out, "The heart of the matter is the fact that there is generally no need to tear the mounds apart in the first place."

Unfortunately, this view is not shared by the local archaeological establishment, notably Professor George Eogan who has been in charge of the reconstruction of Knowth at the Boyne Valley UNESCO World Heritage Site. It seems clear he and some other archaeologists funded by the Irish government still adhere to the outdated mindset which (with only a very few exceptions) tends to downplay, deny, and suppress any research or evidence that some of our megalithic monuments were not only used for burial and ritual purposes, but were also designed as astronomical observatories which still function five to eight millennia after their construction.

Cynthia Austin. Aill na M'reann (the stone of divisions) West Meath. This is the royal heart of Ireland, burial place of the Mother Goddess Eriu, who is symbolically enabled to see the whole of her land and people when the Druidic fires are lit at Bealtaine (May Eve).


Four factors have been proposed to explain this narrow-minded attitude. The first is the unfortunate but common Catholic prejudice against any "pagan" and therefore "heretical" if not "evil" spiritual traditions of the Old Religion – such as the ancient Goddess-cults and Sun-worship of the Tuatha Dé Danaan and of the Celtic Druids who used the sites much later on – which Christian fundamentalism would equate with so-called "witchcraft" and "devil-worship". The second may be banal professional jealousy, perhaps related to the fact that it was the artist Martin Brennan, rather than an archaeologist, whose observation of the solar alignment at Cairn T, Loughcrew made headline news in 1982 because it confirmed that Newgrange was not an isolated case, leading to a live TV broadcast of the Newgrange event last Winter Solstice as part of Ireland's Millennium celebrations.

A third factor may have arisen as a consequence of the alignments measured by the archaeologists in the two passages of the large passage-mound at Knowth, in the Boyne Valley. Because these alignments were found to be very close to the East / West azimuths for sunrise and sunset around the Equinoxes, they constitute a third and fourth example of a solar alignment, following and thus supporting Martin Brennan's earlier discovery at Loughcrew, lending even more weight to the realisation that Newgrange is not an isolated case. Some critics have suggested that the archaeologists in charge of Knowth may therefore have been quite pleased to use the convenient pretext of preserving a souterrain in order to block the Eastern passage with a slab of concrete, thus concealing its alignment from public view and thereby avoiding the inevitable embarassment which would otherwise ensue from having to admit that their ongoing denial of the astronomical dimension in their previous books is simply wrong.

The fourth factor which is undoubtedly in play is the build-up to a scientific paradigm-shift. As Thomas Kühn explained in his book "The Structure of Scientific Revolutions", this occurs throughout the history of Science when new data emerge that do not fit inside the current explanatory system. At first, the data are ignored, and those who espouse them are branded as cranks. But when the volume of unexplainable data eventually reaches the point where the old framework seems obviously inadequate, a new paradigm which can account for the new data emerges and is accepted. Specifically, it appears that the field of Irish archaeology has now come to this point.


After close to 40 years of excavation and reconstruction work, the great cairn of Knowth – the largest of the Boyne Valley mounds known in Irish as Brú na Bóinne (i.e. the Mound of Bóann – the Boyne River Goddess of the Tuatha Dé Danann) – is due to be fully re-opened to the public in the Spring of 2001. Site visits made by concerned individuals in the Autumn of 2000 have resulted in allegations and photographic evidence of the following:

East entrance to Knowth
blocked by concrete slab

"The people will appear to be omniscient, but will generally know nothing." – Socrates


  • The entrance to the 40-meter long Eastern passage has been blocked with a slab of concrete! This precludes any observation of the sunbeam which might otherwise enter the passage and the chamber around the Spring and Autumn Equinox sunrises, thus defeating the very purpose for which the most richly decorated and one of the largest chambered passage mounds surviving from Neolithic Europe was built five and a half thousand ago.

  • An important gnomon (standing stone sundial) in front of the Eastern entrance on the East side of the cairn has not been replaced in its original position, making it impossible to evaluate a key astronomical function of the site (its counterparts in front of the Western passage of Knowth and the passage at Newgrange cast a shadow on the vertical marker of the petroglyphs on the respective entrance stones of those passages, announcing and confirming their astronomical alignments).

  • A concrete bunker and visitor's centre has been inserted inside the mound itself.

  • Real harm may have been done through failing to control the drainage within the cairn by re-using the ingenious original design of alternating layers of natural building materials (clay, earth and stone) which seem to have kept the inner chamber at Newgrange waterproof for five millennia. These have been replaced with a combination of concrete, styrofoam and putty which are hardly appropriate for one of Europe's oldest sacred buildings and which (perhaps due to inadequate testing) are said to result in Europe's largest collection of Neolithic petroglyphic art now being regularly subjected to water damage every time it rains!

  • The ancient Irish megalithic monuments are a global treasure, and their mismanagement is not trivial. If the authorities in charge of their protection continue to deny, neglect and vandalise their astronomical function, as has already happened at Knowth in 2000 and Carrowmore in 2001, we might as well sell the originals to Disneyworld and make do with plastic copies. What do you think?

    Martin Brennan put it in a nutshell: "The mounds are not riddles or follies, they are a living testimony to the indomitable spirit of a Stone Age people, who built not only for themselves, but for future generations".


    Please email your comments to Michael O'Callaghan at or contact him at this address.


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    Updated 1 August 2001
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