The dome—20 feet thick at the base, tapering to 7.5 feet thick at the oculus—is the largest unreinforced concrete dome in the world. This engineering marvel caps a 142-foot diameter rotunda with a perfect hemisphere.
Image by Bjørn Christian Tørrissen
Sourced from Wikipedia
Throwback: The World’s Oldest Monolithic Dome—the Pantheon
CC BY-SA 3.0
Image by Bjørn Christian Tørrissen via Monolithic Dome Institute (CC BY-SA 3.0)