During the excavations of Newgrange in the 1960s and 1970s, Professor Michael J. O'Kelly investigated an area at the rear of the great cairn, opposite the entrance, because several kerb stones on that side had fallen over. What he found is intriguing, and led him to speculate that a structure – possibly a smaller passage-tomb – pre-dating Newgrange might yet be found.
The excavations at Newgrange did not involve digging up the whole structure. The archaeological digging was confined to a wide arc at the front of the monument, from roughly southwest to northeast, centred on the entrance to the known passage-tomb. A further cutting with a total length of 27 metres was made at the rear of the monument, where several kerb stones which had fallen over during the course of time needed to be restored to the vertical. (O'Kelly 1998, pp. 66-67, 91).
When the so-called "north cutting" was made, several things stood out as interesting to the archaeologist. When the "cairn slip" material (stones which had slid off the cairn at some point in the past) was removed, there were very few artefacts compared with the area being excavated on the south side of the monument. When the earth and stone layers were removed, there was no quartz on the ground outside the kerb like had been found on the southern side. Instead, there was a layer of "carefully selected boulders". (O'Kelly 1998, p. 71).
These boulders were not found on a subsoil surface but rather the "sloping surface of a layer of redeposited turves". This layer was thickest at the base of the kerb (65cm) and thinned out further from the giant kerb stones, with a limit or edge 4.5m from the base of the kerb. The kerb stones at this point – numbers 51, 52 and 53 – were found to have been set into sockets which had been dug into the turves forming this mysterious layer. The sockets were then packed with boulders as elsewhere.
Prof. O'Kelly observed that the great kerbs – each weighing between 2 and 5 tonnes – had not been set into a freshly laid layer of turves, but rather the stones were placed there long after the turves had been consolidated. In other words, the turf mound had been there for some time before the great kerb of Newgrange was put in place. (O'Kelly 1998, pp. 71-72).
Another feature that had aroused interest was the vertical groove which is picked into the centre of the surface of kerbstone 52 and continues up over its top edge. Did this stone – with its lavish ornamentation and lying diametrically opposite to the entrance stone which also features a vertical groove – indicate that this part of the monument was significant, and maybe even marked the location of "a smaller passage-grave or other structure under the pre-existing turf mound?" (O' Kelly 1998, p. 72). Such vertical grooves are also features of the entrance kerb stones at the eastern and western passages of Knowth.
The north cutting behind kerb stones 52 and 53 extended as far as 8m behind the back of these kerbs. The profile behind K53 showed that the layer of turves not only continued all the way to the rear of this cutting – it also increased in thickness from 80cm immediately behind the kerb to a height of 1.5m at the farthest limit of the excavated trench.
O’Kelly’s description of the layer of turves at this point (8m behind the kerb) is fascinating, especially with regard to the extraordinary preservation of the vegetation:
Forty-two separate layers of turves could be counted at this point, representing, if our experiments at cutting turves were reasonably accurate, an original minimum thickness of c. 4.2m for the turf mound at this point. When blocks of the turves were cut out they could be easily separated into individual turves along the vegetation streaks and it was surprising to find these were still almost as green as when the turves were cut. Left exposed to the air, however, the vegetation quickly changed colour from green to dark brown. Mosses, grasses and leaves were clearly visible, although pressed flat.
The turf mound, which O’Kelly clearly suggests was an older mound which had been cut into in order to place the giant kerb stones of the larger (and later) main cairn, was around 4.2m high 8m from the rear of the kerb, and the full limit of its size cannot be ascertained because the excavation trench at this point (the north cutting) was limited to 8m behind the kerb. O’Kelly suggested a fascinating possibility:
The increasing thickness of the turf mound running inward under the cairn in this area suggests the presence of an already consolidated turf mound and it is possible that had it been feasible to pursue it farther, a passage-grave or other structure pre-dating the great cairn might have been encountered within it.
O’Kelly’s own magnanimous attitude was that he should not excavate the entire Newgrange monument because archaeology was an evolving science and better methods and technology would be available in the future to fully reveal its secrets.
Such technology was employed at Newgrange in 2011, when a team of Irish and Slovakian archaeologists used multi-method geophysical techniques to investigate the possibility that there are further undiscovered chambers beneath the great cairn.
A report by Thomas J. Westropp in the Journal of the Royal Society of Antiquaries of Ireland in 1893 carried the extraordinary assertion that an unknown passage had been glimpsed inside the 5,000-year-old monument. Westropp wrote:
Capt. Henry Keogh, R.M. of Tralee, writes to me stating that, on a visit to Newgrange, he discovered, between the right-hand recess and that facing the entrance, a passage, once closed by one of the great lining blocks of the central chamber. He says:– “I got my head and shoulders so far in that I was able to see that the passage turned towards the middle of the mound. It was nearly filled to the top with small broken stones and the parts of the large stones forming its sides are covered with carvings and spirals; it evidently leads to another chamber within the mound. Its exploration would probably result in an interesting discovery, and valuable arms and ornaments might be found.”
Unfortunately, the 2011 investigation only investigated the known passage and chamber. “The key objective of the survey was to investigate the potential of the microgravity method in the initial detection of the known chamber and subsequently in searching for possible hidden chambers.” (Barton et al, 2013, p. 32).
The results of their survey showed “a well developed negative anomaly over the centre of the chamber”. The existence of the passageway could not be detected using micogravity, but a multi-frequency electromagnetic survey showed a “significant linear apparent conductive anomaly over the zone of the excavated and reconstructed passage”. (Ibid., p.33).
Having detected the known chamber, the project had fulfilled its initial objective. However, examination of the rest of the mound – the unexcavated parts – has yet to take place. The presence of two passages at Knowth, and at least two at Dowth (there may be more awaiting discovery) leads some archaeologists to speculate that another passage might exist at Newgrange, as yet undiscovered.
In an interview with RTE television in 1962, the year the excavations began, Prof. O’Kelly said:
“The problem is to decide whether this turf mound is of the same date as the cairn and tomb or whether it belongs to an earlier time. This might be a very interesting matter indeed.”
Prof. O’Kelly passed away in 1982. Perhaps some day these key questions will be answered: is the mound of turves in fact an earlier mound, as he suspected? Does it contain a hidden or lost passage and chamber? Is there another passage/chamber structure within the great cairn of Newgrange waiting to be discovered?
These are exciting possibilities.
Barton et al, Searching for hidden chambers at Newgrange Passage Tomb; some results with an evaluation of the multi-method geophysical techniques used, published in Non-Destructive Approaches to Complex Archaeological Sites in Europe: A Round-Up, Frank Vermuelen & Cristina Corsi (Eds.) https://is.stuba.sk/vv/pub_priloha.pl?id=276487
O'Kelly, Michael J. (1998) , Newgrange: Archaeology, Art and Legend, Thames & Hudson.