Pantheon

Rebuilt under Emperor Hadrian in the 2nd century AD (the inscription on the façade honours Marcus Agrippa, who built the first temple), it has a dome about 43 metres across — still the largest unreinforced concrete dome in the world. Since 609 it has been a church, Santa Maria ad Martyres: Raphael and the kings Victor Emmanuel II and Umberto I are buried here.

Did you know: The oculus at the top of the dome is open: when it rains, water falls in and drains through small holes in the floor. On Pentecost, by tradition, rose petals are dropped through the oculus.

✦ The legend: A medieval legend holds that the oculus is the work not of architects but of the devil: forced to flee when the pagan building was consecrated as a church, he is said to have burst through the dome from within. Another tradition tells that the Romans filled the building with earth mixed with coins in order to build the vault, and that the crowd then carried it away basket by basket, hunting for the gold.