There are two main clusters of these features, known as the Ulster Group and the Munster Group. The Ulster group is identified by low lying megaliths (usually under 1 metre), and circles of an irregular number of stones. The Munster group can be identified by tall megaliths (usually over 1m and up to 3m in height), and circles of an odd number of stones (5,7,9,11 etc.).
Standing stones dot the Irish countryside, though not all are of ancient pedigree. Some that appear similar to Bronze Age monuments may in fact be recently erected by farmers as scratching posts for cattle!
Some standing stones that date to the Bronze Age were later re-used in the Early Christian period as bearers of Ogham inscriptions. Ogham is the earliest form of writing found in Ireland, and is a type of writing system thought to be based on the Latin alphabet, though it is quite different in appearance. A series of horizontal and diagonal strokes were used, in combinations of one to five, to make up individual letters, usually carved along the edge of a stone, and read from the bottom up.
The language of Ogham is a version of Goidelic Celtic known as Primitive Irish, the ancestor language of Old and Modern Irish, Manx and Scots Gaelic. Inscriptions are mainly in the form of personal, tribal or ancestral names. The standing stone in Craggaunowen bears such an inscription, which was added in recent years as a reproduction of a fourth century example that is currently housed in the National Museum of Ireland. It says 'Veqroqq Maqi Glunleggett', which means 'Fiachra, son of Glunleggett'.