Ogham

Ogham or the Celtic tree alphabet is a script that was used primarily to write the early Irish language and later the Old Irish language. There are roughly 400 surviving inscriptions throughout Ireland and western Britain, the bulk of which are in southern Munster. All surviving inscriptions are on stone, though it's likely it was also written on sticks, stakes and trees. The vast majority of the inscriptions consist of personal names, used to mark land ownership or tombs.

It's believed the Ogham alphabet was modeled on another script or is merely a cipher of another script. The template script is largely assumed to be the Latin alphabet, though the Runic alphabet and even the Greek alphabet have also been proposed.

Usage
The inscriptions are carved on raised stones, usually inscribed around the corners of rocks. It is written starting from the bottom to the top, then goes over the top of the stone and runs down the opposite side. In manuscripts and in modern use the script can be written bottom to top left to the right, or horizontally left to right, with a line connecting all the letters representing what would be the edge of the stone.

Strictly speaking, the word ogham refers only to the script, while the letters themselves are known collectively as the Beith-luis-nin. Originally Ogham had 20 letters which are grouped into four aicmí ("family" or "class", singluar: aicme). Each aicme is named after its first letter. The fifth aicme was added for use in manuscripts in the Old Irish period, bringing the total letters to 25.

According to the High Medieval Bríatharogam, the names of various trees can be ascribed to individual letters. However, modern Ogham scholars believe the "Tree Alphabet" idea dates to the Old Irish period. It was not used in the Primitive Irish period, or at least the time when the letters were originally named. Its origin is probably due to the letters themselves being called feda "trees", or nin "forking branches" due to their shape. Since a few of the letters were, in fact, named after trees, the interpretation arose that they were called feda because of that. Some of the other letter names had fallen out of use as independent words, and were thus free to be claimed as "Old Gaelic" tree names, while others were forcefully reinterpreted as epithets of trees.

Other symbols
The symbols ᚛ ᚜ are used to mark the beginning and end of a passage. These are only used in manuscripts and modern usage, when writing on stone like the script was intended these would not be used. Ogham is also known for having a "space" character ( ) that is not actually a blank space, this is due to the way Ogham is written on paper, where the edge of the stone is represented by a line.

Hand signals
There is direct evidence for the existence of a system of ogham hand signals where the form of the letters was mimic using the number and position of the fingers. There were two forms: cossogam ('foot-ogham') and sronogam ('nose-ogham'). Cossogam involves putting the fingers to the right or left of the shinbone for the first or second aicmi, and across it diagonally or straight for the third or fourth aicmi. The number of fingers extended determines the specific letter. Sronogam involves the same procedure with the bridge of the nose. Another version, basogam ('palm-ogham') is mentioned which seems to involve striking the hand in various ways against wood.

History
The earliest inscriptions in ogham date to about the 4th century AD and use of ogham in stone inscriptions seems to have flourished in the 5th and 6th centuries. However some believe its origin is as early as the 1st century BC. with a period of writing on wood or other perishable material prior to the preserved monumental inscriptions. The inscriptions may be divided into "orthodox" and "scholastic" specimens. "Orthodox" inscriptions date to the Primitive Irish period. "Scholastic" inscriptions date from the medieval Old Irish period up to modern times.

There are two main schools of thought among scholars as to the motivation for the creation of ogham. Some have suggested that ogham was first created as a cryptic alphabet, designed by the Irish so as not to be understood by those with a knowledge of the Latin alphabet. . The Roman Empire, which then ruled over neighboring southern Britain, represented a very real threat of invasion to Ireland, which may have inspired the creation of a cryptic alphabet. Alternatively, it may have been created in later centuries when the threat of invasion had receded and the Irish were themselves invading the western parts of Britain. The desire to keep communications secret from Romans or Romanized Britons would still have provided an incentive. With bilingual ogham and Latin inscriptions in Wales, however, one would suppose that the ogham could easily be decoded.

The second main school of thought is that ogham was invented by the first Christian communities in early Ireland, out of a desire to have a unique alphabet for writing short messages and inscriptions in the Irish language. The argument is that the sounds of Primitive Irish were regarded as difficult to transcribe into the Latin alphabet, so the invention of a separate alphabet was deemed appropriate.

A third theory put forward by the noted ogham scholar R. A. S. Macalister was influential at one time, but finds little favor with scholars today. Macalister believed that ogham was first invented in Cisalpine Gaul around 600 BC by Gaulish druids as a secret system of hand signals, and was inspired by a form of the Greek alphabet used in Northern Italy at the time. Macalister's theory is a reflection of the fact that the alphabet consists of groups of five letters, with letters being a sequence of strokes from one to five, which could imply that the script was based on hand signals, rather than the other way around.

Another theory, from modern scholars, which tries to explain the letters being in groups of five, is that the forms of the letters derive from pre-existing tally-mark systems, which was then adapted to an alphabet.