THE PANTHEON
The Pantheon was first built in 27 B.C. by Agrippa--hence the inscription above the door "M Agrippa L F Cos Tertium Fecit" (Marcus Agrippa, son of Lucius, third consul, built this)--but it was believed to have burned down in a major fire.  It was rebuilt from 118-135 A.D., by the Emperor Hadrian, who was a big admirer of Greek culture.  He had the orignal roof plated in bronze, and the original bronze doors (still there today) were plated in gold.
The internal geometry of the rotunda including the dome is a perfect sphere: measuring 43.30 meters (142 feet) in diameter as well as height. The wall is 6.05 meters thick, and the cupola ranges from 20 feet thick at the base to 7.5 feet at the top.  
Enter the Pantheon
Back