Celtic Knotwork
Knotwork was not original to the Celts. It was widely practiced thorughout Early Medieval Europe. Celtic knotwork which was their prevalent art form from the 7th - 10th century was by far the most complex. Much of the beauty and complexity of Celtic knots was due to monks who used the knots to embellish their work. A distinctive style was the knot with no beginning or end. a continuum with many meanings. To Celtic Christians the knot would ensnare the devil who would endlessly search for the beginning or the end. This "eternity knot" could symbolize eternal love or faith or life as well. The Triquetra, or Trinity Knot is the best known of all knots. Another popular knot is the Lovers knot representing two together.
While it's hard to know what meanings the ancient Celts assigned to thier knots, a rule of thumb is that circles represent unity or eternity, spirals represent cycles of life and rebirth, triangles the three dominions of earth, sea and sky and four fold shapes were shields or symbols of protection.
Over the years these knots have come to mean many things as people have interpreted them for themselves- such is the vitality of art and the human spirit. Who can say the ancient Celts didn't share many of the same meanings and passions in life?