The interlacing lines of the Celtic Knot stands for "no beginning, no ending, the continuity of everlasting love and binding together or intertwining of two soul or spirits." Christianity has embraced much of the ancient Celtic symbolism and had adapted many Celtic Knots into high crosses and illuminated manuscripts. 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 Book of Durrows. The Celts did not record the meanings behind the designs they recreated  but scholarly speculation is that the symbols represented basic tenants of life, mankind and spirituality. The continual looping of the designs suggests themes of eternity and interconnectedness. Interwoven figures of people and animals may have represented the interdependent nature of life.  Two of more knots laced together symbolized lovers, 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. Circle knot represent eternity or the eternal cycle of life, death and rebirth. Triangles represent the threefold dominion of earth, sea, and sky or God, Son, and Holy Spirit. Square knots are shield knots, symbols of protection. Interlaced animals and men represent relationship, or emphasize the interdependence of mankind and nature.