The Roman temple rebuilt under Emperor Hadrian around AD 126 and crowned by the world’s largest unreinforced concrete dome is the Pantheon.
The present building replaced an earlier temple commissioned by Marcus Agrippa during Augustus’s reign. Hadrian preserved Agrippa’s famous inscription on the portico, which is why the façade still credits Agrippa even though the surviving structure belongs largely to the second century. Its name is commonly associated with “all the gods,” although the building’s original religious purpose remains debated.
The dome spans about 43.3 metres, matching the interior’s height from floor to oculus. Roman builders reduced its weight by varying the aggregate: dense travertine appears lower down, while lighter tufa and pumice were used near the top. Coffering and the nine-metre oculus further reduce the load.
A common mix-up is confusing the Pantheon with the Parthenon in Athens. The Pantheon is Roman, has a domed rotunda, and has served as a Catholic church since AD 609.