The natural world appears and moves in circles. Native American Indians say that the power of the world works in circles and everything tries to be round. The sky is round, the sun, the moon, the planets, birds make circular nests, flowers have circular centres, the seasons come and go in a circular fashion. The deeply significant yin yang symbol is circular representing the balancing of worldly dualities. To the Celtics circles were often drawn as protective boundaries, not to be crossed by enemy or evil.