The Pantheon is the only sacred building of the imperial age completely preserved until today in all its architectural structure
To want this temple, dedicated to the seven planetary divinities, was M. Vespasian Agrippa, son-in-law of Augusto: the building was part of his urban project of 25 B.C. Destroyed by a fire, was completely rebuilt in 120 A.D. by the Emperor Hadrian, who never linked its name to none of the buildings built by him, indeed, in this case, he asked to highlight on the tympanum of the pronaos the ancient inscription that refers to the first manufacturer.
The pronaos is supported by sixteen big columns of gray and pink granite with Corinthian capitals; the portals of bronze remained, the bas-reliefs which adorned the front wall of the pronaos have been lost, because were disassembled and fused by Urban VIII Barberini for Sant'Angelo Castel cannons and part of the of Saint Peter Basilica altar.
In 1658 Pope Clement IX built a grate of iron to put an end to the market, which for generations was installed between the columns.
The diameter of the dome is identical to the inner height, the main niches house the statues of the planetary according the Ptolemaic conception of the universe (Sun, Moon, Mercury, Venus, Mars, Jupiter and Saturn). The dome, large 43,30 m, was the largest ever until the construction of the Church of San Pietro, wider than 78 cm and considerably higher, the fruit of careful studies of Bramante and Michelangelo.
It was built with a process very similar to today's cement, the material was called pozzolana. The wall of the base is often 6 m thick, while at the highest point of the thickness is of 1.5 m and has an opening, at the time coated with bronze, causing a wide beam of light at midday.
The diameter of this "eye" is 9 m. The floor is slightly concave and in the center there are channels that make flow the rainwater.
In the main niche in 1848 was buried Vittorio Emanuele II, first king of Italy, facing the tombs of his successor Umberto l and his wife Margherita, just beside Raphael one.