Croghaun Cairn is located on a cone-shaped peak in the Ox Mountains eight kilometers south of Knocknarea. This small monument, with a diameter of only seven meters and a chamber of less than two meters in length, occupies the whole of the small summit. The chamber is about the same size and shape as many of the monuments at Carrowmore, and the chamber of Cairn O in Carrowkeel.
The monument, which was probably a tertre, the earliest form of passage-grave found in Ireland–a round flat platform with a central, free-standing burial chamber. Croughan was known locally as Diarmud and Grainne's bed, a name commonly given to megalithic monuments, referring to the myth of Diarmuid and Grainne from the Fenian cycles. The area between Croughan and Doomore and the sea is one of the most mythological areas in Ireland, a place mentioned many times in the old annals and manuscripts, Traigh Eothaile, where Eochy, High King of the Fir Bolg died at the end of the First Battle of Moytura. Eochy's cairn, located in Ballisodare Bay, was one of the most famous ancient sites in Ireland, and was considered to be the thirteenth wonder of the world to the medieval annalists.
The gneiss mountain is covered with a thick layer of heather and bog, which has grown since the monument was constructed. One of the reasons that the monument builders were attracted to this hill is that white quartz was plentiful here, and much of the quartz used in Sligo in ancient times may have been quarried here. The hill southern side of the hill is bounded by a partial enclosure which may date to the neolithic.
Archaeologist Stefan Bergh excavated a trench across this chamber, and recovered some charcoal which produced extremely early dates, stretching back over 8,000 years. While the megalithic monument itself probably dates to around 3,500 BC, the charcoal indicates that the hilltop was used for fires back in the mesolithic, before the Anatolian farmers arrived in Sligo around 4,100 BC.
Megalithic Survey Report
Some tqo kilometers south of Ballysadare Bay on the narrow summit of Croaghaun Mountain which commands an extensive outlook in all directions. A southeast-facing undifferentiated passage tomb of rectangular outline (Length 1.7 meters; Width 0.95 meters) stands in a circular cairn (diameter 7 meters; Hright c. 0.6 meters). Three stones form the left-hand side of the structure, one stone of a probable original three stands at the right-hand side and it is closed by a backstone. A sillstone stands at the front of the chamber.
The site was excavated in 1985 (Bergh 1986, 35; Bergh 1995, 104-5, 225). Cremated human bone was found in the chamber and also a fragment of a poppy-headed antler/bone pin, one piece of chert with wear-marks and fragments of a coarse ware pottery. Five minor deposits of cremated bone were found in the cairn with one of which there were sherds of food vessel type. A hollow scraper made of chert was also found in the cairn. During the excavation two displaced slabs, likely to have been chamber roofstones, were found south and west of the structure.
Radiocarbon dating of charcoal from an in situ cremation suggest it was deposited in the interval 5640 to 5490 BC (calendar years). This date is much earlier than would be expected for a passage-tomb so it may be that charcoal already many centuries old somehow became associated with the burial deposit. Charcoal associated with cremated bone in another part of the chamber has been dated to the interval 4675-4460 cal. BC. This date too, according to the excavator, presents 'problems of interpretation'.
A prehistoric wall (Width 3-8 meters; Height c. 1 meter; Length c. 175 meters) of large boulders, which may have been associated with the passage tomb, lies c. 130 meters to south where it curves around the base of the mountain roughly southeast-southwest.
Sitting on the summit of Croughan is somewhat like being on the top of a natural pyramid, with the sides of the hill falling away steeply in all directions. There is a tremendious view from the tiny chamber, which is 170 meters above sea level. Many important neolithic sites are intervisible from here: Carrowkeel and Kesh Corran Knocknashee and Muckelty Hill, Doomore Cairn nearby, Knocknarea Carrowmore and Carns Hill, and the group of cairns on Sliabh Da Ean to the east.
While visiting one evening near sunset close to an equinox in the late 1990's, I got to witness the shadow projected by the cone shape of Croughan. The mountain casts a pyramidal shadow, like a huge pointer, which streyches out and becomes longest at sunset.