The characters themselves are known collectively as Beth-luis-nin, after the first letters of the groups, similar to the way Greek Alpha and Beta gave us the ‘alphabet’. Each Ogham letter is associated with a plant or tree, and a particular sound, and represents a collection of ‘kennings’; keys to knowledge, called the Briatharogaim.
While the texts and tales frequently mention Ogham being carved on wood and bark - used for spells and to record genealogies - it is the 358 inscribed stones known to remain in Ireland which provide a more permanent record. These seem to have served as burial or commemoration stones, boundary markers, and even a legal record for who might hold title to the land on which they stand.
It is impossible to definitively date the language, as we have no certain fixed points in history, archaeology, or linguistics. Most will agree that the Ogham carved stone tradition dates at least back to the 300’s CE, coinciding with the coming of the Latin language to Ireland, through trade with Roman Britain and the scholarship of Christian monks. Whether this was the start of the script, or it has deeper Pagan roots, is a question that waits to be answered.
Ogham’s importance in a hero’s burial is immortalised in the Táin:
“Then Etarcomol’s grave was dug
And his headstone planted in the ground
His name was written in Ogam
And he was mourned.”