The marriage-knot or knot of Hercules, a strong knot created by two intertwined ropes, originated as a healing charm in ancient Egypt, but is best known for it’s use in ancient Greece and Rome as a protective amulet, most notably as a wedding symbol, incorporated into the protective girdles worn by brides, which were ceremonially untied by the new groom. This custom is the likely origin of the phrase “tying the knot.”
According to Roman lore, the knot symbolized the legendary fertility of the God Hercules; it probably relates to the legendary Girdle of Diana captured from the Amazon Queen Hippolyta. In this, the marriage-knot was probably a representation of the virginity of the bride.
The symbolism of the knot survived well beyond its religious use, and was a very common symbol in medieval and Renaissance love tokens.
Greek girdle, 3rd cent. BCE