The name Pantheon is dedicated to the memory of great Frenchmen.
Pantheon is dedicated to planetary Gods(Mercury, Venus, Mars, Saturn, Pluto, Neptune, Jupiter,at that time, Uranus hadnt been discovered).
Agrippa was the front part designed in the first century B.C. The original Pantheon was a rectangular temple, consisting of sixteen single granite columns. The emperor Hadrian (A.D. 118-128) decided to rebuild it.
When the Romans learned to use concrete, they were able to mold on the ground their rounded tops , and in this way they changed their buildings.
The Pantheon is a structure with an opening at the center top of the dome. Oculus is an eye (in latin) in the center of the dome. A drain at the center catches the rain when is necessary to protect, because the floor is concave.