A TREASURE TROVE of megalithic art imagery from a recently uncovered passage tomb is being released to mark the winter solstice.
The Dowth Hall tomb is part of the Brú na Boinne complex, and is located a stone’s throw away from the more famous Newgrange, Knowth, and Dowth tombs.
It was hidden underground until an excavation in 2017. What remains was damaged by the construction of a building above it in the 18th century.
The find was described as ‘the most significant’ of the past 50 years in Ireland.
An estimated one-third of the kerbstones – which would have surrounded the tomb – and orthostats – upright stones – found at Dowth Hall are decorated in Neolithic art.
The Discovery Programme, an archaeological research group funded by the Heritage Council, has now documented a selection of the art found at the site, created moveable 3D models, and made them available to the public.
The team involved used a technique called structure from motion (SfM) photogrammetry, which involves taking a series of high-quality photographs of the stones using carefully calibrated cameras. It is then processed to create a high-resolution 3D model, capturing its geometry.
As many as a thousand images might be needed to photograph a single orthostat.
Robert Shaw, a senior geo-surveyor with the Discovery Programme, told The Journal this technique is by no means simple, but it is more accessible and less expensive than other methods such as laser scanning, although can produce better results depending on the intended purpose of the scan.
“What we’re trying to do is get these models recorded at the highest resolution we can so that we can use these visualisation techniques to help the archaeologists increase their understanding of the site,” Shaw explained, adding that the researchers have access to even higher quality models which are used to assertation exactly how some features were created.
The resulting 3D model can be rotated and allows light to be cast on it in any direction, meaning previously unknown features can suddenly be discovered, as the markings can sometimes be easily overlooked by the naked eye.
This is not uncommon. Megalithic art at the Hellfire Club in Dublin was found by chance when low autumn sun struck it at the correct angle.
And more recently, carvings on rocks at a well-known stone circle in Limerick went unnoticed until a photographer specialising in capturing prehistoric art came across them.
Dr Clíodhna Ní Lionáin, lead archaeologist on the Dowth Hall dig, said this is where the value of these models lies, allowing you to explore the art in more detail under a range of lighting conditions. She herself only noticed some of the more subtle art at Dowth Hall when the sunlight at a particular time of year hit the rocks.
“It shows the benefits of always keeping an eye out when you’re visiting these sites, because you never know what you might see,” she said.
For me, that’s the important thing about getting these models open and accessible to the public, that people can look at them and might spot things that we don’t.
She added that The Discovery Programme’s other collections – such as scans from Knowth, Newgrange, Omagh stones and high crosses – make it a “great resource for the country”.
The art at the site fits into the repertoire of other Boyne Valley passage tombs, although all have their own unique features, Ní Lionáin said.
One (T1.9) features a particularly large design consisting of a stacked chevron motif, above two horizontal lines, below which there are three inverted V-motifs.
Ní Lionáin notes that similar motifs have been found in Wales at the Barclodiad y Gawres passage tomb and also in Portugal, and believes it may represent an important location within the tomb as you pass from the outside to the interior.
Another is T1.3, where the use of different techniques can be seen.
“On the south face of that stone, you’ve got a natural shelf, and underneath the shelf, they’re using a technique known as pecking, and we’ve got a circle and a dot, and then 17 dots radiating out from it.
Then above that shelf, they’re only using incised techniques. We’ve got a series of incised and radial lines. So they’re using this natural transition on the stone to distinguish between the different techniques.
The other side of the stone is very smooth, with some striations likely caused by glacial movement during the ice age, but the carvers who worked on the stone have pecked them out further to emphasise this effect.
“The geology and shapes of the stones were really important to them – it wasn’t simply a canvas to them.”
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