The interior dome and walls of the Pantheon, in Rome, Italy.
The structure known today as the Pantheon was originally constructed by Marcus Agrippa during the reign of Augustus. The present building was restored or completed by the emperor Hadrian.
Remarkably, the Pantheon has been in continuous use since the 100’s CE, when it was likely dedicated by Hadrian in 126. Since the 7th century, it has been used as a Catholic church.
The dome of the Pantheon is still the largest un-reinforced concrete dome in the world, and forms a perfect half-sphere.