The triquetra is the simplest possible knot. It is three intersecting lenses that connect in such a way that they are formed from a single continuous line. It is another never-ending path, like the labyrinth or the spiral.
The triquetra symbol is very common in Celtic art, especially in metalwork and illuminated manuscripts such as The Book of Kells. It was not seen in Celtic art until the seventh century, however, and is by no means unique to Celtic artwork. It is found on northern European rune stones and early Germanic coins. The symbol had a pagan religious meaning and it may be significant that it is similar to the Valknut, a symbol of the god Odin.
The triquetra is rarely allowed to stand on its own in medieval Celtic art, which has led some to say that it was probably never a primary symbol of belief Its main role appears to have been to fill a space or as an ornament within more complex compositions. In knotwork panels, the triquetra often appears as a design motif But these observations overlook the fact that the triquetra is a very simple design that incorporates both the rule of three and the never-ending path. In Celtic minds this must have given it a certain power.
In the Christian period, the triquetra has seen use as a symbol of the Holy Trinity, especially in and since the nineteenth-century Celtic revival.
A very common development of the triquetra is its combination with a circle. The circle emphasizes the unity of the combination of the three elements of the triquetra. As such, it makes a perfect symbol of the Holy Trinity, the Three-in-One and One-in-Three, “God in three persons.” In neo-pagan beliefs, the triquetra is seen as symbolizing the three stages of the Triple Goddess: maiden, mother, and crone.
In modem times, the triquetra is often used as a pattern in jewelry, such as a necklace or ring. Here is it seen as representing three promises inherent in a relationship, such as to love, honor, and protect. The knot is commonly engraved on wedding rings. In neopagan groups, especially Celtic Reconstmctionist groups, the triquetra is used to represent one of the many triplets or triads in the belief system.
Such as the three-fold division of the world into land, sea, and sky, or one of the Triple Goddesses (see Labyrinth, Rule of Three, Spiral).