Classification
Old Irish was the only member of the Goidelic/Gaelic branch of the Celtic languages which is in turn a sub-family of the wider Indo-European language family that also includes Slavonic, Italic/Romance, Indo-Aryan, Germanic sub-families and a few less well known ones. Old Irish is the ancestor of all the modern Goidelic Langues; they are Modern Irish, Scottish Gaelic and Manx.
A still older form of Irish is known as Primitive Irish. Fragments of Primitive Irish, mainly personal names, are known from inscriptions on stone written in the Ogham alphabet. These inscriptions date from about the 4th to the 6th centuries. Primitive Irish appears to be very close to Common Celtic, the ancestor of all Celtic languages and has a lot of the characteristics of other archaic Indo-European languages.
Read more about this topic: Old Irish