The Trinity

13th century
Church of St. Agatha, Perugia, Italy

The artist references the doctrine of the Trinity (three persons in one God) by giving a single figure a threefold face. This iconographic type continued in use from time to time but was condemned by Molanus in the 16th century and prohibited by Urban VIII in the 17th.

Read more about images of the Trinity.

Source: this page at Wikimedia Commons.