Roman engineering at its best: the 2000 year-old Roman temple called the Pantheon

Pantheon
Originally uploaded by dranidis

The Pantheon ("temple consecrated to all gods") is a building in Rome, Italy, says Wikipedia, commissioned by Marcus Agrippa as a temple to all the gods of Ancient Rome, and rebuilt by Emperor Hadrian in about 126 AD.[2]

The building is circular with a portico of large granite Corinthian columns (eight in the first rank and two groups of four behind) under a pediment.

A rectangular vestibule links the porch to the rotunda, which is under a coffered, concrete dome, with a central opening (oculus) to the sky.

Almost two thousand years after it was built, the Pantheon's dome is still the world's largest unreinforced concrete dome.[3] The height to the oculus and the diameter of the interior circle are the same, 43.3 metres (142 ft).[4]

The inscription across the front of the Pantheon says:
M·AGRIPPA·L·F·COS·TERTIVM·FECIT
meaning "Marcus Agrippa, son of Lucius, made this building when consul for the third time."

The grey granite columns that were actually used in the Pantheon's pronaos were quarried in Egypt.

. Hidden chambers engineered within the rotunda form a sophisticated honeycomb structure.[35] This reduced the weight of the roof, as did the elimination of the apex by means of the oculus.

Throughout the day, the light from the oculus moves around this space in a sort of reverse sundial effect.[40] The oculus also serves as a cooling and ventilation method. During storms, a drainage system below the floor handles the rain that falls through the oculus.