If you only have time for one ancient building in Rome, make it the Pantheon. A 1,900-year-old temple that makes architects go quiet and first-time visitors stand in the middle of the floor staring at the ceiling. The story is the best one Rome tells: a building that refuses to fall down, on engineering nobody fully understands.
How the Pantheon was built
Hadrian built the Pantheon you walk into today around 125 AD, on the bones of two earlier temples that burned down. The inscription across the portico, "M. AGRIPPA L.F. COS. TERTIUM FECIT," credits Marcus Agrippa, who put up the original in 27 BC. Archaeologists are clear that Hadrian rebuilt the whole thing. He kept Agrippa's name up anyway, which reads as humility or a flex depending on the day.
The dome is the reason any of us are here. 43.3 metres across. The world's largest unreinforced concrete dome for over 1,300 years, and it still holds the record. No rebar, no steel. Roman concrete, poured with brains: heavy travertine and tufa near the base, lighter volcanic pumice up by the oculus. Five rings of 28 coffered panels take weight out of the dome and pull your eye up. The walls at the bottom are more than 6 metres thick. By the time you reach the oculus, they're down to 1.2.
The oculus
At the top of the dome, a round opening 8.7 metres across is the building's only light source. No glass, never has been. Rain falls through. The floor curves a fraction with drainage holes you'd miss if you weren't looking, which is why it isn't a puddle. On sunny days, a beam of light tracks across the walls like a spotlight that forgot to hurry. At noon on April 21, the traditional founding date of Rome, the beam lands on the entrance doorway. Was that intentional? The Romans never wrote it down, but I choose to believe it. The oculus also earns its keep structurally: a solid dome this size would be heavier and crack at the crown. The hole takes the stress off the weakest point.
Raphael's tomb and what else is inside
There are several important tombs in the Pantheon. The one most visitors look for is Raphael's. He died in 1520 at 37, which still hurts to type. Find his tomb in the third niche on the left, behind a Madonna sculpture by Lorenzetto. The Latin inscription translates as: "Here lies Raphael, by whom Nature feared to be outdone while he lived, and when he died, feared she herself would die." It's the most moving epitaph in Rome. Two Italian kings rest here too (Vittorio Emanuele II and Umberto I), along with the painter Annibale Carracci.
See the Pantheon with a local guide
The Pantheon is a key stop on our morning Classic Rome tour. Our guides explain the engineering secrets and hidden details you'd miss on your own.
Why the Pantheon survived when other temples didn't
In the Middle Ages, builders stripped most Roman temples for parts. Marble went into new churches. Smiths melted bronze down for cannons and church furniture. The Pantheon survived because in 609 AD, Emperor Phocas handed it to Pope Boniface IV, who consecrated it as the Church of Santa Maria ad Martyres. As an active church, no quarrymen touched it. It didn't escape clean, though. In 1625, Pope Urban VIII (a Barberini, remember the name) ordered the bronze ceiling of the portico stripped to make cannons for Castel Sant'Angelo and the baldachin inside St. Peter's. The Romans, who never miss a good pun, coined the phrase "Quod non fecerunt barbari, fecerunt Barberini." What the barbarians didn't do, the Barberinis did.
Visiting the Pantheon: what you need to know
Entry now requires a timed reservation booked online through the official site, or you can chance the queue if open slots remain. Go early morning, right when it opens at 9, or late afternoon when the crowd thins and the oculus light turns gold. Midday packs in the most people, but the light beam peaks then too. If it's raining, run there. Watching rain fall through the oculus and evaporate off the warm floor is one of the strangest, best moments Rome offers. The church holds Mass on Sundays and holy days, which limits access during services. Photos are fine.
The piazza and what's around it
Piazza della Rotonda, out in front, is worth lingering in. Giacomo della Porta designed the fountain in 1575, and someone parked an Egyptian obelisk on top of it in 1711. Honest warning: the cafés on the piazza will rip you off. Beautiful view, inflated bill. Walk one street back and your espresso drops to a normal Roman price. Behind the Pantheon, the Church of Santa Maria sopra Minerva sits overlooked. Inside: a Michelangelo sculpture (Cristo della Minerva) and a Filippino Lippi fresco cycle. Most visitors walk straight past the door. A minute further and you reach Piazza di Sant'Eustachio, which many Romans (including me) will tell you serves the best coffee in the city.
Architects from Brunelleschi to the designers of the US Capitol have copied this dome. None of them beats it. Stand under the oculus, look up, and you'll see why. Nearly two thousand years in, no Roman building answers the question better.
