Ogham, also known as the Celtic tree language, was an amazing written communication method used by the Celtic/Irish people in the 4th century. It has been difficult for historians to piece together this language because of the secrecy surrounding the Druids. The Ogham alphabet is the earliest known form of writing in Ireland, a practice usually held by the Druids. Druids were essentially the scholars of Ireland. It took years for them to train, but when they graduated, they were often called upon by rulers and Kings as advisors to world problems.
The origin of the word "Ogham" is speculative but it has been linked to Irish mythology. It is associated with the name Ogma, who were/are a race of god-like individuals of the Tuatara de Danaan. Ogma was a Sun god who invented the language of Ogham.
(Ogham Stone, Dunloe, County Kerry, Ireland.)
Ogham originally had 20 letters and later five more were added for a total of 25 letters. The letters were a combination of lines that were read from bottom to top. An inscription looked similar to a tree growing with the letters as branches. Each letter correlated with a tree sacred to the Druids. The letters were grouped into five 'families'.
Today, we can find Ogham inscriptions on stones, the most famous being that of Stonehenge. Stonehenge is a grouping of stones standing in a circle that pose a mystery in and of themselves. There are those today that use Ogham as a form of divination. The letters are carved onto a piece of wood, usually the correlated tree of the symbol, and then consulted with life questions. Ogham rune sets are tools to communicate with otherworldly Beings or with the tree Spirits.
Here is a list of trees sacred to the Druids:
Birch, Rowan, Alder, Willow, Ash, Hawthorn, Oak, Holly, Hazel, Apple, Vine, Ivy, Reed, Blackthorn, Elder, Silver Fir, Furze, Heather, Poplar and Yew.