THE PANTHEON DOME
The Pantheon’s dome is one of the most remarkable feats in engineering history — and it’s nearly 2,000 years old. Built during the Roman Empire using unreinforced concrete, it remains the largest of its kind.
To support such a massive structure, Roman engineers used a brilliant mix of materials: heavy stone at the base, light pumice near the top, and coffers (sunken panels) to reduce weight. At the center? The oculus — a 30-foot-wide opening that lets in light and rain.
The dome isn't just impressive for its size — it’s a lesson in load distribution, material science, and symmetry. It was also built to last: the secret Roman concrete mix is so strong, modern engineers still study it today.
Engineering Lens: Lighter at the top, stronger at the base. Material matters.
Memory trick: Remove weight where you can — especially up high.
What to remember
- Largest unreinforced dome: built around 126 AD, still standing.
- Concrete mix matters: heavy to light gradient keeps balance.
- Coffers lighten the load: decorative *and* structural.
- Oculus relieves pressure: and lets in light — no glass needed.