Pantheon

The present building was raised by Emperor Hadrian around AD 125, though the pediment still carries the inscription of Agrippa, who built the first one. The dome is 43 metres across, exactly the same as its height, and it is still the largest unreinforced concrete dome in the world.

In 609 it became the church of Santa Maria ad Martyres, which is why it has survived so well. Inside are the tombs of Raphael and of Italy's first kings. When it rains, water falls through the oculus and drains away through small holes in the floor.