The document discusses the Pantheon in Rome. It was originally built in 27-25 BC by Marcus Agrippa but burnt down in 80 AD and was reconstructed by Hadrian in 125 AD. The Pantheon has the greatest Roman temple circular plan with a 142 foot diameter concrete dome with an oculus to let in light. It showed cultural diffusion and its dome structure is still the largest unreinforced concrete dome ever built.