An Irish writing system, the Ogham alphabet, was developed in Ireland by at least the 4th Century (300s CE, Common Era), to express and represent the sounds of one of the first forms of the Irish Language, known to scholars as Primitive Irish. 

The Ogham alphabet has survived in it's earliest known form carved into Ogham Stones. The height of use was during the Classical period, from the 5th to 7th Centuries CE. used to mark land boundaries and to write personal names. The alphabet's design was such that it could be carved into stones.

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What was the Ogham alphabet used for?

Its primary purpose during the Classical period was to record names, but previous to that it may have also served as a form of secret or even magical communication.

The orthodox inscriptions on stones bearing the names of landowners became proof of ownership. These Ogham stones typically stood near the boundary of the land they owned. As a result, these stones likely became the boundary markers of families, or even Túatha, and their territories.

Later, in the Scholastic tradition, Ogham was recorded for academic purposes in Christian manuscripts, which changed its form and function somewhat. 

The Ogham alphabet outside of Ireland

This is one of the most ancient forms of writing, and it is thought to have been used in writing the Irish language before it was adopted for use in other European cultures. The Ogham alphabet is found on standing stones throughout Ireland, Scotland, England, Wales, and Brittany.

There are approximately 500 surviving orthodox Ogham stones, 400 of which remain in Ireland.

According to Irish mythology, the Ogham alphabet was created by the Tuatha Dé Danann god Ogma, who has a Gaulish counterpart in the god Ogmios, a lord of the Underworld who is said to have been able to lead the souls of men through the power of his tongue.

The connection between either Ogma or Ogmios to the Ogham alphabet however, remain something of a mystery, if we go only by the remaining Medieval literature. 

Letters of the Ogham alphabet

The alphabet consists of twenty letters in it's original use, with an extra 5 (or 6) coming into use in later periods. Ogham was first carved on stone (and perhaps on wood or other permanent items, even earlier).

We read it from bottom to top, and follow the main stemline or central edge from left to right if it conitnues across the top, and down the other side. 

Etched around this vertical stemline we find the ogham alphabet, a series of horizontal lines or notches. 

From 'Ogham in 3D':

The characters are made up of between one and five lines or scores relative to a stemline, generally vertical on stone using its natural angle or edge, with two of the groups distinguished by the orientation of the scores to the stemline. The third group transverses the stemline diagonally and the fourth group consists of one to five scores or notches on the stemline... "

There are four groups of letters, called Aicme in Irish (plural, Aicmí).

• The first aicme contains the letters B, L, F, S, N, and the letter stroke faces to the right.
• The second aicme contains the letters H, D, T, C, Q, and the letter stroke faces to the left.
• The third aicme contains the letters M, G, nG, St, R, and the letter strokes cross diagonally.
• The fourth aicme contains the letters A. O. U, E, I, and the letter strokes either go straight across the stemline, or are represented by notches instead. 

A fifth group, called the Forfeda (extra letters) are seen later in the manuscript tradition, but the only one of these that appears with any regularity in inscriptions on stone shows up as two diagonal scores crossing each other on the stemline, in the shape of an X. This is usually given the sound value of a hard K.

Watch Lora's video on source materials for the Ogham alphabet