The Pantheon is one of the oldest buildings in Rome.  It has been  beautifully preserved by the Catholic Church since the 600's.  Mass is still celebrated there.   Luckily, we got to see it in both daytime and at night.

 

Do you see that black little square above the window in the photo below, and in the one at the very top?  That is the hole that Brunelleschi cut in the dome to try and figure out how the concrete was poured!