From looking at the outside of the Pantheon I sure wouldn’t have guessed it was this extravagant on the inside. It looked as if it was built only a few years ago not a thousand years ago!
“On entering the door, the effect you feel is meant to be overwhelming. You suddenly find yourself in this huge empty space which causes vertigo and makes you feel tiny. This is how you were supposed to feel in front of the gods and anyone going in today can have the same sensation as the Romans did almost 2000 years ago.
The space is a perfect sphere symbolising the vault of heaven; the height of the dome is the same as its diameter creating perfect balance and unique harmony; it is round so as to place all gods at the same level of importance.
Surrounding you, placed in seven splendid niches between two Corinthian columns the used to be the seven gods linked to the worship of planets, or considered to be such: the Sun, the Moon, Venus, Saturn, Jupiter, Mercury and Mars. With the advent of Christianity, some of them were used for small altars dedicated to Christian Martyrs.
The Pantheon’s greatness mainly comes from its mighty dome, still today the biggest brick dome ever built. Raising it using bricks alone would have been impossible; the ceiling would not have withstood the weight and would have collapsed.”
Reference: Italy Guides