Ogham commonly understood as the ancient Irish 'tree alphabet', ogham was first recorded on stone monuments from the 1st - 6th century and later by monks in the 6th - 9th centuries recording earlier lore. It was most likely created by and used exclusively by the druids, in its earliest times for the marking of graves and monuments, but also for oracles by the branch of druids known as the filid, or oracular poets whose task was to be the memory keepers, the guardians of ancestral and traditional lore. Ogham for them was a symbolic and magical system which used the example, image and metaphor of the trees, and their energies to signify and open up whole vistas of meaning accessible only to a magically elite and learned few.  It also features in many Irish myths as a magical sytem of lore and divination.  Although each ogham letter corresponds to a tree, and in the 20th century was given the added correspondences of months in a tree calendar by Robert Graves, their meaning is not limited to the tree they represent, but can be unlocked over time by meditation on the tree and associated quatrains and kennings contained in the few surviving texts that provide the sum of knowledge on the ogham, especially the 7th century ‘Scholars Primer’.  However, these symbols have a power of their own, as well as their unique spiritual energies, which can be invoked for simple divination or magical purposes.  They are divided into five aicmi (tribes). Sometimes a further five, the forfeda are included but they are a much later addition to accommodate consonants not included in the Irish alphabet.