The Brú na Bóinne prehistoric landscape in the valley of the River Boyne in Ireland is recognized as one of the great Neolithic treasures of the world. It is best known as the site of the largest and most richly decorated of the Neolithic structures known in archaeology as the Passage Tomb. These are very large structures built by the Neolithic civilisation which existed in Ireland about 5000 years ago (according to results of radio carbon dating). The most famous of these is the Newgrange (irish Gaelic:
Sí an Bhrú ) passage tomb which is located on a small hilltop on the south bank of the Boyne. Newgrange is familiar to many due to the fact that its sole passage was aligned to the sunrise on the winter solstice of the Northern Hemisphere, a phenomenon that can still be observed today by those present inside the chamber on the five days around the shortest day of the year.
But how many know about its sister site called
Knowth (irish gaelic: Cnóbha) located in the northwest of this prehistoric landscape? It may come as a surprise to many but the complex at Knowth, dominated by what is the largest passage tomb in Europe and which is surrounded by at least nineteen smaller passage tombs, is even worthier of the fame which Newgrange has gained over the years. Such was the extent of the rich archaeological features uncovered by the excavation team under the guidance of state archaeologist, Prof. George Eogan, that it took almost forty years to excavate. Those excavations uncovered evidence for at least twelve different phases of human activity at Knowth. These extend from the late Neolithic and early Bronze Ages to the post medieval periods with a major exception being the remainder of the Bronze Age and early Iron Age for which there was no evidence of human activity discovered. I don’t wish to get into detail about all of these discoveries (and there is a lot!) but rather focus on one phenomenon which can be observed at the entrance to the western passage of the great mound at Knowth at the time of the Equinoxes, days of equal day and night.
The two passages at Knowth are aligned due East and due West, back to back, but they do not meet inside the tomb. Each passage terminates with its own chamber, the western chamber is of a type known as undifferentiated, basically a much simpler box type chamber. The eastern passage, which is 40 metres long, ends with the more complex cruciform style with side recesses familiar to many visitors to Newgrange. Unlike the single passage at Newgrange the two passages of the great tomb of Knowth are not accessible to visitors. But I’ve been fortunate as a guide working there to have the incredible privilege to be allowed once inside both of the passages. The journey inside to the great Eastern chamber is not for the faint-hearted. To reach the chamber you have to squeeze through with your body on the ground turned sideways due to the partial collapse of some of the large stone orthostats lining both sides of the passage. Inside is a truly amazing sight including the most beautifully carved basin stone in the right recess. The western passage is less of a challenge but no less awe-inspiring.
Both passage entrances have a large kerbstone which has different rectilinear megalithic art to the other 125 kerbstones lining the base of the tomb at ground level. Each entrance stone, as they are called, is inscribed with a vertical line grooved into the stone and it aligns with the center of the passage behind.
Laid out on the ground are stones of smaller size including quartz and water rolled granite stones. But right in front of the Western entrance stone stands a 2-metre-high standing stone or menhir made of red sandstone. Due to the position of the menhir in relation to the other smaller stones Professor Eogan believes that this stone was raised for special purposes at certain times of the year or for ceremonies around the monument. He found the socket of the stone and positioned it in its upright position. This is in line with the vertical groove in the entrance stone and the Western passage. At the time of the Equinoxes in March and September, and only at this time, these two large stones combine to present a phenomenon that I and other guides have often observed.
Around 6pm in the afternoon, as the sun begins its slow descent to the western horizon, the shadow of the menhir travels across the face of the entrance stone. It starts to the left of the entrance stone and moves to the right. After about half an hour its shadow is at its most prominent over the vertically incised groove in the center of the entrance stone. After about an hour it moves away from the face of the stone. The journey of the evening shadow is most clearly seen around the day of the Equinoxes, usually 21st or 22nd of March and September. The shadow can be seen in the days after the Equinox and then it moves away as the days become shorter or longer, as the case may be.
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The photographs of the shadow of the Autumnal Equinox at Knowth are my own, so you can see what I’ve just described. Is it just a coincidence or by design? Considering George Eogan is satisfied that both these large stones are in their original positions I tend to think it’s by design.
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There’s something else that’s worth noting about this menhir. The surface of the stone on all four sides is rough. But it is smooth on both sides and on the back at about the three-quarter height stage, roughly corresponding to shoulder height. George Eogan believes that this smoothing was achieved by human hand rather than by environmental action on the stone.
Strangely, you won’t find any mention of the Equinox shadow of Knowth in official literature but, from these photographs taken during the Autumn Equinox and from my own observations, you can be sure that it’s quite real.
Autumnal Equinox in the Northern Hemisphere is on Tuesday, 22nd September 2020 at 13:30 UTC.
A special time for Éiriú Eolas.
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