Ogham (Celtic alphabet)

Ogham (pronounced ohm) is an alphabet used for Old Irish between the 4th and 7th centuries CE. Its form is unique in the history of writing: each letter is composed of carved notches along the edge of a standing stone, read bottom to top and then left to right when the inscription wraps around the corner.

More than 400 ogham inscriptions survive, mostly in southwest Ireland, Wales, and the Isle of Man. They almost always come from funerary stelae or boundary markers, recording the deceased’s or owner’s name in just a few letters.

Principle

The four aicmí

The original ogham alphabet has 20 letters divided into 4 groups (aicmí, pronounced ekemi) of 5 letters each:

Aicme Beith (B-aicme)  : B  L  F  S  N    — notches on the right
Aicme Huath (H-aicme)  : H  D  T  C  Q    — notches on the left
Aicme Muin (M-aicme)   : M  G  Ng Z  R    — diagonal strokes across
Aicme Ailm (vowels)    : A  O  U  E  I    — short transverse notches

Each letter is identified by:

• The side of the stem (left, right, or both for diagonals).
• The number of notches (1 to 5).

The “forfeda”

In the 9th century, 5 extra letters (forfeda) were added to transcribe sounds absent from the original Old Irish: Ea, Oi, Ui, Io, Ae. They use more complex graphic combinations (crosses, open squares).

The extended alphabet then contains 25 letters, enough to cover virtually all Old Irish phonemes and Latin loanwords.

Why this strange shape?

Several hypotheses on the origin of ogham:

1. Cryptographic origin — Macalister (1937) argued that ogham was originally a secret cipher used by druids or bards for confidential messages. Recent analysis (McManus, 1991) leans rather toward:

2. Linguistic adaptation — the alphabet was designed to transcribe Old Irish using an economical medium (stone, carved with axe or chisel), where simple notches are faster to cut than curves.

3. Latin influence — the grouping into fives may reflect awareness of the Latin alphabet (B, L, F, S, N = the first five common consonants, etc.). But the decision to favour notches is probably Gaulish/Celtic and pre-Christian.

Famous inscriptions

• CIICUS MAQI MUCOI HUNALI (Cnoc na Manach, Ireland) — of Cíocus, son of the Hunal clan, c. 500 CE.
• VOTECORIGAS MAQI VICTORI (Wales) — of Votecorigas, son of Victor, mixing ogham with Latin lettering.
• Pillar of Knockboy — the longest inscription (60 characters), now partly eroded.

These names almost always follow the formula X MAQI Y (“X son of Y”), making them immediately decipherable by crib.

As a cryptographic device

Although probably not designed as a cipher, ogham is now used as a themed monoalphabetic substitution in:

• Celtic- or fantasy-themed escape rooms.
• Tabletop role-playing games (D&D, Pathfinder) — druids use ogham as a secret tongue.
• Fiction — The Lord of the Rings and several fantasy novels riff on ogham for their fictional alphabets (Cirth, runic Tengwar).
• Modern jewellery and tattoos — the Celtic revival of the 1990s–2000s brought ogham back into fashion.

Its table has been public since the 19th century, so no real security. Its value is cultural and aesthetic.

How to decode by hand

1. Identify the vertical stem (the central line, or the stone’s edge).
2. Count the notches on each side or across.
3. Identify the aicme: right only (B-aicme), left only (H-aicme), diagonal (M-aicme), short transverse (vowel).
4. Read the position within the aicme (1st to 5th notch).
5. Look up the letter in the beith-luis-nin table.

About 30 seconds per letter at first, fluent reading after a handful of attempts.