Ogam, or Ogham, (pronounced OH-am) is an ancient Celtic divinatory system based on the Celtic alphabet. It is, more specifically, Druidic. Irish mythology states that the Ogam alphabet was invented by the god, Ogma (also called Cermait). He was one of the Túatha dé Danaan. Unfortunately, there is not much about how it was created, other than he is a god of the Druids. The Ogam has twenty letters, though five were added later. The letters, read from the bottom up, are called fews, and they are separated in four sets, or aicme, of five: Beith, Huath, Muin, and Ailm. The additional set of five is called the forfeda. According to some sources, instead of the forfeda there were four symbols, called the Treasures, which are unlike the other twenty-five. Traditionally, Ogams are carved into the corresponding tree branch, although that can prove to be difficult and many times they are carved on alder.