When we get the question "How Many Ogham Letters Are There?", our standard response would be - 20. Those are the ones we use regularly, the original 4 groups or Aicmí.

This is correct for the original phase of ogham inscription, when the alphabet was carved on stones, which is often called the Classical, or Orthodox period (4th/5th to 7th Centuries CE). 

Ogham is Ireland's oldest written script, and while it was used between the fourth and seventh centuries as outlined above, it then went on to gain a 'second life' during the Scholastic period. This is the Ogham which began to be written in manuscripts by Christian monks, in Medieval Ireland.

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Originally, the groups were twenty letters in all, and these symbols were divided into four blocks of five, as laid out in the image above. 

As the Irish language developed through time, more letters were needed to represent the varying sounds of Archaic and Early Old Irish, so the Forfeda or 'extra letters' were created within the manuscript tradition.

See the video for more details!