Cairn D is the largest monument at Loughcrew, with a diameter of about 55 meters. Along with Heapstown Cairn and Queen Maeve's Cairn in County Sligo, it is one of the largest unopened chambered cairns in Ireland. It has always been one of my favourite cairns because it is so mysterious; so much effort was spent digging for a chamber, but none has yet been found.
The west side of the cairn, where there is a fallen quartz pillar, may well have a chamber like those in Dowth: very small for the size of the mound.
Cairn D and Cairn L are the two focal monuments on Carnbane West, but despite being only 200 meters apart, niether can be seen from the other. Cairn D is very tall and would have had a flat top before it was damaged, which would have been used to observe the heavenly bodies rising and setting across the landscape around Loughcrew.
During his work at Loughcrew in 1865, Conwell made two attempts to locate the entrance. On one session he spent nearly two weeks with a group of labourers digging through the cairn. They dug a great trench through the mound beginning on the south east side where the kerbstones curved inwards, usually an indication of an entrance. Many tons of stone were removed, but the chamber was never found.
As with Macalisters excavations in Carrowkeel in 1911, Conwell did not leave the site as he found it, and the massive cairn lies peeled open.
He gave up and decided that the monument must be a cenotaph - a view later endorsed by George Coffey. Cenotaphs, or blind cairns are monuments without chambers, perhaps used as memorials or markers. However, it is highly unlikely that the Loughcrew builders would put so much effort into such a massive cairn and leave it blind. As with Queen Maeve's Cairn in County Sligo, only excavation will reveal a chamber in this greatest of the cairns at Loughcrew.
On the opposite side of the cairn to Conwell's excavation lies a massive chunk quartz, which appears to be a fallen standing stone as the stump can be clearly seen in the ground. There are traces of quartz on this side of the cairn too - chunks peep out of the grass around the kerbstones. This quartz pillar probably marks the entrance to the mound, which could be oriented roughly to the summer solstice sunset.
There is a triangular kerbstone which may well prove to mark the entrance if the mound is ever excavated. Standing stones mark the entrances to several other large cairns including Newgrange and Knowth. A similar fallen pillar stone lies about the same distance away from Heapstown Cairn in County Sligo.
This has been the largest of all the carns in the range, the diameter of its base being sixty yards.
The north and east sides have been left untouched but on the south and west for nearly 100 yards round the base, and extending inwards to a distance of twenty-four yards from the circumference towards the centre, the dry loose stones composing the carn have been entirely removed.
The height of what remained of the carn, before commencing any operations upon it, measured twenty-eight paces in sloping ascent from the base to the summit. The original circle of fifty-four large flagstones, laid on edge round its base, is still perfect; and on the eastern side these marginal stones curve inwards for twelve paces in length towards a point indicated by E. 20° S., denoting where the entrance or passage to the interior chambers is to be found.
As the carn at this point—which, judging from the analogy in the construction of the other carns, would indicate the direction of the passage—appeared not to have been previously disturbed, Mr. Naper and Mr. Hamilton had from the first strong hopes of finding the interior chambers and their contents in their original state, such exactly as they had been left in by the builders of this megalithic pile.
Accordingly, on Monday morning, 4th September, 1865, about a dozen labouring men commenced to remove the stones, and to make a passage inwards from this point. As they advanced in this way into the carn, the loose stones composing it occasionally fell in dangerous masses, filling up excavations already made; so that it was at length determined to make a cutting right through the carn, running east and west, and commencing on the top.
After two weeks spent in this labour, with as many men as could be conveniently engaged at it, we did not come upon any of the interior chambers; nor have our labours been more successful on 3, 4, 5, 6, 8, 9, and 10, June, 1868, when, by Mr. Naper's directions, twenty men were busily engaged every day in continuing the transverse cutting through the carn, in search of the interior chambers. This, however, is now the only one of all the carns left un-examined; and, as the surface level of the ground has been already seached for the greater part of the way across the carn, very little additional labour would be required to settle the question whether or not this is a " blind tope."
As the cutting proceeded, about midway down among the loose stones, were found portions of skulls, teeth, and other bones of graminivorous animals, probably the ox and deer.
At a distance of 105 feet to the north-west of this carn, and on the very point of the escarpment of the hill, stood a pillar of quartz, eight feet high, three feet broad, and two feet thick. How far it may have entered the ground when being placed there originally, we have not ascertained. At present it is broken across a little above the ground, probably by lightning, and the upper portion now lies as it fell.
At a very slight cost it could be raised to its original erect position, which we would very much desire to see.
Whatever the case may turn out to be, Cairn D still holds onto its secrets.