The "Borromean rings" are a sign of unity in diversity. The name, “Borromean,” comes from the use of this three ring design in the coat of arms of St. Charles Borromeo's northern Italian family. In mathematical knot theory, the Borromean rings are a simple example of a Brunnian link: if you break one link, the entire knot comes apart. The link itself is much older and has appeared in the form of the valknut on Norse image stones dating back to the 7th century. The Borromean rings have been used in different contexts to indicate strength in unity, e.g., in religion or art. In particular, the design has been used to symbolize the Trinity.