Fiorenzo Laurelli (Twitter) published some interesting images on the sun in the Roman Pantheon.
In occasion of the Equinox he shows the light of the sun falling in this amazing temple. He is also providing an interesting reference of this subject: Il Pantheon come strumento astronomico, Fausto Masi, International EILES, 1996 .
Let us remember that the Pantheon is a building made of concrete. For more information on ancient concrete, see please my paper at the link http://www.ijsciences.com/pub/article/412