Historians claim that the origin of the Ogham alphabet is estimated to have originated from the 4th century of the common era.
There are theories that the alphabet was possibly named after the Irish god Ogma but this is debated widely. Ogham was used for etching the Irish and Pictish languages on stone monuments.
There are records that suggest that it was also used for writing on pieces of wood, but there is nothing to evidence this.
Description of Ogham
In its most basic form, ogham consists of 4 sets of strokes or notches.
In a set, there are five letters composed of from one to five strokes.
In total, there are 20 letters.
These letters were cut into the edge of a stone, either from top to bottom or from right to left.
A fifth set of five symbols, called forfeda (“extra letters”), appears to be a later development in the language.
Where Ogham is found
There are roughly 400 – 500 ogham inscriptions throughout Britain and Ireland with the most appearing in Pembrokeshire.
Other sites where the inscriptions were found were around south-eastern Ireland, the Isle of Man, Scotland, and Orkney. Ogham was used to write in Archaic Irish, Old Welsh and Latin, and the inscriptions with Ogham that have survived are almost all personal names and marks of land ownership.
Amazingly, in Shetland, ogham has been discovered and has actually been used to write Norse words such as dattur (daughter) and krosk (cross).
Equally astounding, in Killaloe, Co. Clare, a stone has a commemoration from around the year 1100 CE dedicated to a settler, Torgrim. The Stone is inscribed with Norse runes and also, repeated again in ogham.
Origin of Ogham
There are 4 main theories discussing the origin of Ogham.
First origin theory of Ogham
Scholars such as Carney and MacNeill suggest that Ogham was first created by the Irish as a cryptic alphabet.
A secret language used for political, military, and religious reasons to keep information away from those who could just read in Latin.
Second origin theory of Ogham
Scholars such as Mcmanus argue that Ogham was invented by the first Christians in early Ireland in a quest to be unique. Every civilization wants to have their own special language, and this was no different in early Ireland.
The argument was that the sounds of the Irish language were too difficult and foreign-sounding, for the regular language of the time – Latin. 
Third origin theory of Ogham
The third theory is that Ogham was invented in West Wales in the 4th century BCE to combine the Latin alphabet with the Irish language.
This was done as a response to the marriage between the Romans and the Britons.
Historians think that this theory may be accurate as it would account for the fact that some Ogham inscriptions are bilingual; meaning that when they are pronounced, they spell out Irish and Brythonic-Latin.
Fourth origin theory of Ogham
The most mythical of all the theories, this one states that Ogham was invented in Cisalpine Gaul around 600 BCE by Gaulish Druids.
It was created as a hand signal and oral language and was finally put into writing in early Christian Ireland. Historians argue that the lines incorporated into the Ogham scripts actually represent the human hand by being based on four groups of five letters.
However, there is no evidence for this theory that Ogham came from Gaul.
Other mythical theories for the origin of Ogham also appear in texts from the eleventh to fifteenth centuries. In the eleventh-century book Lebor Gabala Erenn it states that Ogham was created soon after the tower of Babel fell.
The fifteenth-century text Auraicept na n-eces also repeats the same thing, however, the sources of this information is unknown, leading one to speculate that it could possibly be taken from the previous book.