WHAT'S YOUR CELTIC TREE SIGN AND WHAT DID THE DRUIDS SAY ABOUT YOU? The Celtic Zodiac is based on the cycles of the moon. The year is divided into 13 lunar months with a tree assigned to each month. The Druids (the educated, professional class of the Celtic people) believed that the time of our births is pivotal to the formation of our personality and behaviour and the Celtic Zodiac was developed from their knowledge of earth cycles and their reverence for the sacred knowledge held by trees.