The Pantheon is the best-preserved monument of ancient Rome, built around 125 AD under the emperor Hadrian on the site of an earlier temple. Originally dedicated to all the Roman gods, it has served as a Christian church since the 7th century, which helped ensure its remarkable survival.
Its most astonishing feature is the vast coffered concrete dome — still the largest unreinforced concrete dome in the world — crowned by a circular opening, the oculus, that floods the interior with a single shaft of daylight. The dome’s height equals its diameter, a harmony that has influenced architects for nearly two thousand years.
Inside rest the tombs of the painter Raphael and two Italian kings. Entry now requires a timed ticket, and the building remains an active basilica, so sales pause during Mass. Visit near opening to see the light move across the marble before the crowds arrive.