No passage-tomb under Millmount?

Millmount might not have been built on a Stone Age passage-tomb, a public presentation of archaeological data heard last night in Drogheda.

However, one intriguing possibility based on the results of advanced archaeological techniques is that it might perhaps have been built on a clay mound, like a barrow, a type of burial monument dating to the Bronze Age, and therefore later than the likes of Newgrange, Knowth and Dowth.

Millmount might have been built on an ancient burial mound.

But it's still too early to say for certain what lies beneath the mound of Millmount, if anything. The new data is from the latest phase of the Millmount Archaeological Remote Sensing project, aptly shortened to MARS, because some of the technology being used is out of this world!

The presentation was given by Kevin Barton of Landscape and Geophysical Services (LGS), Conor Brady of the Department of Archaeology, Dundalk Institute of Technology, and Brendan Matthews, the Old Drogheda Society Community Historian.

The data presented last night was generated using Ground Penetrating Radar (GPR) and Electrical Resistivity Tomography (ERT). The GPR data was taken along eight transects of the mound, and Kevin Barton revealed that the signal "was totally absorbed" by the mound, indicating that it might consist largely of clay. This would seem to rule out the possibility that it is a cairn, built largely of stone, like Newgrange, Knowth and Dowth. There was a possibility of a slight "overlapping of layers" of clay in the mound, but this was by no means definite.

The Electrical Resistivity Tomography (ERT) data was perhaps the most exciting. This involves putting stainless steel electrodes into different parts of the mound and measuring the resistance based on Ohm's Law (Resistance equals voltage divided by current). A series of measurements were taken at the base of the mound, just above the modern revetment wall, spaced at 5 metres apart. There were four distinct "high resistance" areas along the perimeter of the base of the mound, with low resistance areas underneath them. Eighteenth century drawings show that Millmount had four towers around its base, and these four areas of high resistance might correspond to the location of those four towers.

Four sections of the mound were also measured using ERT, and Kevin Barton revealed results from these measurements which appeared to show a quite distinct area of low resistance at the core of the base of the mound. He said this area of low resistance would correspond in his mind to a large clay mound. However,  he said he could not rule out the possibility of a "cavity" in the interior - something like a passage-tomb or maybe a cist grave.

It would not have been uncommon for Bronze Age barrow to be built over a burial, which sometimes might be contained in a cist grave. This is basically a "box" consisting of large slabs of stone.

Community Historian Brendan Matthews suggested that a Bronze Age barrow-type mound might tie in with the mythology of the site, and that as the reputed burial place of Amergin, the figurehead of the Milesians who landed at the Boyne Estuary, a Bronze Age date might be more apt.

Earlier in the night, Conor Brady of DkIT gave an overview of the types of mounds found in Meath and Louth, including passage-tombs, barrows and a large number of unclassified mounds.

Brendan Matthews revealed that a small section of what might have been an earlier revetment wall, set back some distance from the modern wall, was found during a recent "cleaning up" of the site. He also showed a photo of a stone-lined drain which was found near the top of the mound.

Millmount as it looked in the 1740s, drawn by Thomas Wright.

He revealed that no major modifications had taken place at Millmount from around 1672 until the British fortified the site and built the martello tower on top of the mound in 1807-8. But in the mid 1780s a ditch around the base of the mound was filled in, and local people used it for gardening!

The presentation provoked a lot of questions from the audience, and there's no doubt it has focused minds on the possibility that Millmount is not a passage-tomb, and not, as suggested locally, contemporary with the great mounds of Brú na Bóinne.

However, there have been several people who reported in the 20th century that they had been inside a tunnel under Millmount, and so it is obvious from contemporary accounts that there is at least one subterranean passageway in there. Whether this is part of a passage-tomb structure, or maybe a medieval souterrain, or even perhaps tunnels built linking the 17th century towers is a matter of conjecture right now.

At this point, the Old Drogheda Society will be discussing the possibility of moving on to the next phase of the project, which involves a seismic technique that measures the response of sound waves through the monument. That could provide a more definitive overview of the mysterious mound of Millmount.

First passage-tomb discovered in the Boyne Valley for two centuries using new archaeological techniques

The first passage-tomb to be discovered in the Boyne Valley in 200 years has been identified by archaeologists using sophisticated imaging techniques.

The newly discovered mound, with circular enclosure,
shown on a colour LiDAR image. Reference: Boyne Valley
Landscapes Project. Data: Meath County Council/
Discovery Programme

Archaeological imaging and geophysics specialist Kevin Barton spoke about the discovery, made originally in 2010, at a recent Heritage Week presentation at the JFK Arboretum in County Wexford. He was giving a talk about possible new monuments discovered in LiDAR (Light Detection And Ranging) imaging of the Great Island area of Wexford.

The “new” passage-tomb, on the floodplain of the Boyne southwest of Newgrange, had showed up as a “blip” on LiDAR imagery of the valley, Mr. Barton said. Because of its situation in proximity to the Boyne monuments, it was considered that the feature warranted further investigation.

The newly discovered monument shown in gradiometry with
resistance overlay. The dark linear feature running from SSW-NNE
is believed to be a passage. The small dark circular area is the
mound. The outer enclosure is also faintly visible. © Davis et al

The site was given the designation “LP2” by investigating archaeologists. In the LiDAR image it appeared there was a central mound with a circular outer enclosure feature. The enclosure was “faint but identifiable” in the image.

Further work, in the form of ground-probing techniques called Magnetic Gradiometry and Resistivity was carried out, and revealed what appeared to be a weakly defined outer enclosure in addition to a distinct passage/chamber arrangement of the passage-tomb aligned towards the north-northeast.

Archaeologists became excited about the central mound, which they said “appears to show a clear passage and chamber arrangement with splayed terminals at the NNE. The central mound is clearly identifiable and measures c. 30m in diameter. This strongly suggests that the feature represents a hitherto unknown passage tomb.”

Kevin Barton demonstrating archaeological surveying
techniques at the JFK Arboretum. © Anthony Murphy.

Kevin Barton told the audience at his Co. Wexford talk that he believed it was the first passage-tomb to be discovered in the Brú na Bóinne complex in over 200 years. What makes the discovery very special is the fact that no archaeological digging took place to find it. It was discovered purely through LiDAR imaging and ground-probing techniques.

The area where the passage-tomb is located is close to the Boyne, straddling a modern hedgerow. The land has been under tillage and pasture at various times, and has probably been considerably ploughed over the years.

Commenting on the discovery, Anthony Murphy, author of Newgrange: Monument to Immortality said that it was just one of a number of exciting new features identified over the past few years in the Boyne Valley.

“This is incredible work by archaeologists using an array of new techniques. They have found a passage-tomb that has been hidden in the landscape for millennia, and they have found it without putting a single trowel into the ground.”

This is a wider LiDAR image of the Boyne Valley. The location of the new
monument is shown by the red circle. Map: Boyne Valley 
Landscapes Project. Source of data: Meath County Council/Discovery Project.

“I am particularly excited by the suggestion that the passage of this newly-discovered monument may point towards the north-northwest. If that’s the case, there are two possibilities which I’d like to see examined. One is that the passage points back up the slopes of the valley towards Newgrange. The second is that, because it points to the north-northwest, it cannot be aligned on a sunrise or moonrise, and one could propose a stellar alignment," Mr. Murphy said.

“It’s obviously far too early to say whether that’s the case. But I would definitely be interested in finding out whether there might have been an alignment to Deneb, the bright star of Cygnus, the swan constellation. The Brú na Bóinne area is linked with significant swan mythology. Indeed the owner of Newgrange, Aonghus Óg, was said to have taken the form of a swan. And the fields where this newly discovered mound is located have been the wintering ground for the whooper swans, which have been coming to Newgrange in large numbers for many decades, and possibly since the time Newgrange was built.”

But this newly-discovered monument might never be excavated. Kevin Barton said in his talk that archaeological digging is not only invasive, but destructive.

The new electronic arsenal employed by archaeologists is, however, providing the means to look under the soil without ever having to dig. And Mr. Barton said the equipment and the analysis of data were improving all the time. The new breakthrough is a testament to the exciting prospects of discovery in future of monuments that are currently hidden from view in the landscape.

Some of these new techniques have been employed at the Hill of Slane, where a mound, also surrounded by a circular enclosure, is thought by some to have originally been a passage-tomb, possibly as old as Newgrange, which was later re-fashioned by the Normans into a defensive motte.

Some new techniques will also be employed to examine the possibility that Millmount, in Drogheda, is also an ancient passage-tomb which was re-used by the Normans and later by the British who fortified the mound with a martello tower on top.

Acknowledgements: Steve Davis, Conor Brady, Kevin Barton and Will Megarry (archaeology); funded by the Heritage Council (INSTAR); Meath County Council (LiDAR imagery); the archaeologists are very grateful to the Redhouse family for access to the land.

Boyne Valley Landscapes Project: Steve Davis, William Megarry. Conor Brady, Helen Lewis, Thomas Cummins, Loreto Guinan, Jonathan Turner, Colman Gallagher, Tony Brown and Robert Meehan.

See Boyne Valley Landscapes Project Phase III Summary Report and Phase III Final Report.