The Pantheon has the largest unreinforced concrete dome in the world, and it has held that record for around nineteen hundred years. Nothing built since in unreinforced concrete has matched it. It is also, since 2023, no longer free to enter, which catches out a lot of visitors working from older guidebooks.
The Dome
The building you walk into was completed under Hadrian around AD 126, replacing an earlier Pantheon by Agrippa, whose name Hadrian left on the portico inscription rather than his own.
The engineering is the reason to stand still for ten minutes:
- The dome is a perfect hemisphere, and its diameter equals the height from floor to oculus, both about 43.3 metres. A sphere of that diameter would sit exactly inside the building. That geometry is the whole design.
- The concrete changes as it rises. The mix at the base uses dense travertine aggregate; further up it shifts to lighter tufa and brick, and near the top to pumice. The dome gets progressively lighter toward the crown, which is how it stands.
- The walls thin as they climb, from around six metres at the base, and the coffering both decorates and removes weight.
- The oculus is open. Nine metres across, no glass, never has been. Rain falls straight through onto a floor that is slightly convex, with drainage holes cut into it that still work.
Why It Survived When Everything Else Did Not
Rome’s ancient buildings were quarried for stone and burned for lime throughout the medieval period. The Pantheon escaped because in AD 609 it was consecrated as a Christian church, Santa Maria ad Martyres, and continuous religious use meant continuous maintenance. It is still a functioning church, which is why there is a dress code and why services interrupt visiting.
It did not escape entirely. The bronze that once covered the portico ceiling was stripped in the seventeenth century under Urban VIII, a Barberini pope, prompting the Roman quip quod non fecerunt barbari, fecerunt Barberini: what the barbarians did not do, the Barberinis did.
Raphael is buried here, at his own request, along with the first two kings of unified Italy.
Practical, Including the Change People Miss
- Entry now costs around €5 for adults. It was free for centuries and became ticketed in July 2023. EU residents under 25 pay a reduced rate, under-18s are free, and it remains free for those attending Mass.
- Book online to skip the queue. The line moves but can be long in the middle of the day.
- Go when it rains. This is the single best piece of advice about the Pantheon: watching a column of rain fall through the oculus and vanish into the floor drains is the thing you will remember.
- Or go at noon around 21 April, Rome’s traditional founding date, when the sunbeam through the oculus aligns with the entrance doorway.
- Dress code applies: shoulders and knees covered, as in any Roman church.
- Twenty minutes is enough unless you sit down, which you should.
Pantheon Tickets & Tours
Skip-the-line entry and guided visits are widely available, and many combine the Pantheon with Piazza Navona and the Trevi Fountain.
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Where to Stay
The centro storico around the Pantheon puts most of Rome’s baroque core within a ten-minute walk.
Frequently Asked Questions
Is the Pantheon still free to enter?
No. It became ticketed in July 2023 and now costs around 5 euros for adults, with reductions for EU residents under 25 and free entry for under-18s and for those attending Mass. Older guidebooks still say it is free.
Is the Pantheon’s oculus open to the sky?
Yes, and it always has been. The nine-metre opening has no glass. The floor beneath is slightly convex with ancient drainage holes that still carry the rain away.
Why is the Pantheon so well preserved?
It was consecrated as a Christian church in AD 609, and continuous religious use meant continuous maintenance while other ancient buildings were quarried for stone. It is still a working church.
How is the dome still standing?
The concrete mix changes as it rises, from dense travertine aggregate at the base to lighter tufa, brick and finally pumice near the oculus, and the walls thin as they climb. It remains the largest unreinforced concrete dome in the world.
