Carrowkeel

Known locally as ‘the Pinnacles,’ the Carrowkeel cairns are 15 miles south of Sligo on ridges in the Bricklieve Mountains. Fourteen cairns are found in the Carrowkeel complex, and on the northern slope of the eastern ridge is a cluster of ‘hut circles’ known as the Doonaveeragh Neolithic village. The Carrowkeel complex, believed to have been constructed between 3000 and 2000 BC, remained in use until 1500 BC. The cairns, built of limestone with interior chambers roofed with large limestone slabs, range from 25 to 100 feet in diameter. The site was used in Christian times as a burial place for unbaptized children. Carrowkeel was rapidly and poorly excavated in 1911, often using dynamite, and each cairn was assigned an identification letter.

Studied by the archaeoastronomer Martin Byrne, Cairn G has a lightbox above its doorway, which functions similarly to the lightbox at the enormous passage cairn of Newgrange. This lightbox allows the sun's light to enter the cairn for a month on either side of the summer solstice and the moon's light to enter for a month on either side of the winter solstice. The cairn opens toward the most northerly point of the setting moon, a point which is reached only once every 18.6 years. From Cairn K, the sun can be seen to set on both Samhain (also known as ‘All Saints Day’ at the beginning of November) and Imbolc (the beginning of the Celtic year on February 1), behind the sacred mountain of Croach Patrick, 75 miles away to the southwest in county Mayo. At the rear of Cairn K is a particular rock, known as the Croach Patrick Stone, whose outline closely resembles that mountain. These facts again show that the megalithic builders of ancient Ireland were keen observers of the celestial realm.