The Celts, inhabitants of Northern Britain which is called Caledonia, glorified the power of live and it's creators in which the male and the female principles were both equal and in harmony. For the Celts, live itself was the driving power in the universe. The power that reveals the highest wisdom and everything divine in it's varieties. Death just played a subordinated role. It was just a short interruption in the forever ongoing and always changing cycle of life.
Therefore typical celtic tattoos are devoured ornaments, complicated and twisted knots and spiral motives mostly done in black. Those symbols demanded a very high understanding of mathematics and geometry and were used by the irish monks in the early middle ages, from the 4th until about the 10th century after christ, for drawings in books and they were also found on monuments. Monuments made out of stone like the so called celtic crosses.
Faithful to the celtic believe the celtic cross symbolizes the unity of the opposite spheres. Up and down for heaven and earth and left and right for male and female. And the circle, the perfectly closed form and the divine symbol for the forever ongoing cycle, underlining this union.
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