An ancient Celtic symbol, the triquetra is considered one of the oldest; dating back to as early as 500 BC when it was used to symbolize the triple goddess (maiden-mother-crone). Over the centuries it has become the symbol for the Holy Trinity among Christians in Ireland. The symbol is often used to represent the 3 fundamental elements – air, water, and earth or the infinite cycle of life. It is also known as a rune of protection.
In modern times, the triquetra symbol has become a favorite design element in knot-work, jewelry, emblems, logos etc. as a symbol of anything three-fold e.g. the cycle of life (life-death-rebirth), the promise of a husband to his wife (love-honor-protect), the family (father-mother-child), the passage of time (past-present-future) and many more. The circle that is often interlaced with the triquetra represents the bond between the three elements.