Celtic knots date back to the 5th century and were used extensively by ancient monks in illuminated manuscripts such as the Book of Kells and the Book of Durrow. The Celts did not record the meanings behind the designs they created but scholarly speculation is that the symbols represented basic tenants of life, mankind, and spirituality.
The continual looping of the design suggests themes of eternity and interconnectedness – “no beginning, no ending, the continuity of everlasting love” and “binding together or intertwining of two souls or spirits.” As the Celts believed in reincarnation, some interpret Celtic knots as various lives of one soul woven together on its path to light. Interwoven figures of people and animals may have represented the interdependent nature of life. Two or more knots laced together symbolize lovers, hunters and their prey, God and man, and so on. Some ancient Celtic symbols have changed in meaning over time, having been influenced by the introduction of Christianity and the influence of other cultures. Christianity has embraced much of the ancient Celtic symbolism and has adapted many Celtic knots into high crosses and illuminated manuscripts.
A general rule of thumb is that the shape of the design often determines the meaning of the knot. Circles represent eternity or the eternal cycle of life, death, and rebirth. Triangles and trefoils represent the threefold dominion of earth, sea, and sky. Squares or four-sided shapes are shield knots, symbols of protection from spirits. Interlaced animals and men represent relationships, or emphasize the interdependence of mankind and nature.