Its original meaning was simply "triangle" and it has been used to refer to various three-cornered shapes. Nowadays, it has come to refer exclusively to a certain more complicated shape formed of three vesicae piscis, sometimes with an added circle in or around it. The triquetra is often found in Insular art, most notably metal work and in illuminated manuscripts like the Book of Kells. The fact that the triquetra very rarely stood alone in medieval Celtic has cast a reasonable doubt on its use as a symbol in context where it was used primarily as a space filler or ornament in much more complex compositions. But Celtic art lives on as both a living folk art tradition and through several revivals.