There are many shapes of crosses. The Latin cross, the commonest, has an upright longer than its transom. With two transoms it is called an archiepiscopal or patriarchal cross; with three it is a papal cross. A cross widely used by Slavs and by others of Eastern rites has two transoms and a slanting crosspiece below. The Greek cross has equal arms. St. Andrew's cross is like an X, and the tau cross is like a T. The Celtic, or Iona, cross bears a circle, the center of which is the crossing. The Maltese cross and the swastika (an ancient and widely diffused symbol) are still more elaborate.