Decoding the Pantheon

Ancient Roman monuments hide a secret code. Learn how to decode Roman buildings. In many Roman monuments, the sun is used to mark a special date. The famous Pantheon in Rome is also a vast sundial of a Roman type called a hemicyclium, consisting of the inside section of a hemisphere, with a hole for light to enter, marked with lines delineating the hours. In a hemicyclium, a circle of sunlight marks the hour rather than a shadow as in gnomon type sundials. At the equinoxes, the sun shown half over the dome cornice of the Pantheon. On the anniversary of the founding of Rome on April 21, the sun shown on the massive double doors where the emperor would enter and perform a ceremony. What a spotlight!