One of the best known aspects of the neolithic cairns is the 'passage grave art', a mysterious symbolic language that ornaments many stones, especially in the Boyne Valley and at Loughcrew in County Meath. These engravings are the earliest writing or inscription in Ireland, carved by descendants of the first colonising farmers who landed in County Sligo in the years before 4,150 BC.
A few simple carvings have been found in the western sites: Listoghil, the central monument at Carrowmore, in the chamber of Cairn B at Carrowkeel and on a kerbstone at Heapstown, with what are probably Iron age carvings at Cloverhill near Carrowmore.
The simple western art connects the sites at Lough Arrow and Carrowmore to Loughcrew and the Boyne Valley, part of a common language of symbols used by the cairn builders. Robert Hensey:
As a result of these new finds there is now megalithic art known from all four major passage tomb complexes. While there seems to be a tradition of making megalithic art at passage tombs in County Sligo, it would be wrong to expect large undiscovered quantities of art in the north-west. The authors carried out a two-week search as part of the Carrowkeel Passage Tomb Art Project at many other passage tombs in the Carrowkeel-Keashcorran complex and a number of other passage tombs in the region, and the second stone in cairn B was the only additional art found.
It is likely, however, that more art will be discovered in the west in time. The possible use of pigments to make coloured motifs and designs might also explain the smaller quantities of carved art on passage tombs in the west. Evidence of the use of colour has recently been discovered on the parietal walls at Barnenez and Gavrinis passage tombs in Brittany, France, and at the Neolithic Ness of Brodgar site in the Orkney Islands. It may be that similar evidence will one day be found on the walls of passage tombs in Carrowkeel and on Neolithic monuments elsewhere in Ireland. But that, as they say, is another story.
Conclusion from Once Upon a Time in the West.
There are several boulders at Carrowmore where natural faults and cracks in the rock seem like early inspirations for megalithic art. They are called intrusions and were created when the gneiss boulders were being formed. However, modern research has connected the Sligo monuments to the Brittany area, where there was a tradition of megalithic art before 4,000 BC.
These engravings may well deal with ritual astronomical themes, demonstrated at several sites where the artwork is illuminated by the light of the sun or moon at a chosen time in the cycle of the body in question. This is demonstrated at Listoghil in Carrowmore, Tara, Cairns L and T at Loughcrew and the large mounds in the Boyne Valley.
Knowth alone has 50% of the engraved stones in Ireland. Early engravings have been discovered in recent years on the chamber of Listoghil monument at Carrowmore in Co Sligo. Heapstown Cairn, also in Sligo is known to have had several engraved stones, with perhaps an ogham stone standing at the top of the mound. Only one stone remains visible today, as many were robbed from the site in the last century.