Ogham is the oldest known form of written Irish, first appearing between the 4th and 6th centuries CE. It was used primarily in Ireland but is also found in western parts of Britain, particularly in areas with strong Irish influence such as Wales, the Isle of Man, and southwest Scotland. The script is made up of linear strokes or notches, typically carved along the edge of a standing stone or piece of wood. Each group of marks represents a letter from an alphabet originally consisting of 20 characters.

The origins of Ogham are closely tied to a period of significant cultural change in Ireland. Although Ireland was never part of the Roman Empire, there was contact between the Irish and the Roman world—through trade, migration, and military service in Roman Britain. Many scholars believe that Ogham developed as a response to these interactions, particularly as a native system of writing influenced by the Latin alphabet.

Evidence supporting this theory includes the fact that the earliest Ogham inscriptions coincide in time and geography with Roman Britain, and that the system is alphabetic, a concept likely introduced through Roman literacy. However, Ogham does not resemble Latin visually. Instead of letters written across a page, Ogham letters are made of straight lines and notches grouped along a vertical or horizontal line—often the natural edge of a stone. This design suggests it was created with carving in mind, rather than writing on parchment or papyrus.

The language used in the earliest Ogham inscriptions is known as Primitive Irish, the ancestor of Old Irish and, eventually, modern Irish and Scottish Gaelic. These inscriptions are mostly personal in nature: names of individuals, sometimes along with kinship terms or tribal affiliations. The content is brief, formulaic, and consistent—suggesting that Ogham had a practical purpose, likely tied to property rights, burial markers, and territorial claims.

One key feature of early Ogham inscriptions is their physical location. Most are found in the southern and western parts of Ireland, often in remote rural landscapes. They are frequently placed near boundaries, ancient roads, or burial sites, reinforcing the idea that the script had legal or ceremonial functions.

There are also mythological and medieval references to Ogham found in later Irish manuscripts, where the script is described as being used by Druids or as a system of secret communication. These accounts are much later—often from the 12th century onward—and reflect a reimagining or reinterpretation of the script in a Christian and literary context. While they provide insight into how Ogham was viewed in medieval Ireland, they are not reliable sources for understanding its original development.

Although Ogham's everyday use was relatively short-lived, its creation marked a significant step in the history of literacy in Ireland. The fact that it was developed outside the Roman world, tailored to the Irish language, and adapted to local needs—like carving into stone—makes it a remarkable example of early script innovation. The stones remain where they were first placed, weathered but legible, offering direct contact with a time when marking a name in stone was one of the few ways to be remembered.