The Pantheon Dome and its Amazing Structure! With Linda Seymour PhD

The Pantheon in Rome is a breathtaking space! At 2,000 years old, it’s also the world’s largest unreinforced concrete dome! So how has it lasted so long?

I’ll show you around the Pantheon, explain how domes work (and how much the Pantheon is a full structural dome), and Linda Seymour provides detail on Roman concrete. Linda did her PhD at MIT on ancient Roman concrete and we both work at SGH in Boston so it’s great to have her be part of this!

I'm Paul Kassabian. I'm a structural engineer and a Principal at SGH in Boston, MA. I taught graduate students at MIT for nine years, Harvard's Graduate School of Design (GSD) for five years and am currently teaching at RISD (Fall 2023). These are videos based on my structural design projects and years of teaching structures to students.

MUSIC:
Note: I chose music with instruments that existed in Roman times (harp and voice)

Publisher: Taylor Brook Music. Composer: Taylor Brook. PRO: SOCAN IPI#: 602881067
Title: Spiritual Harp and Choir.
License : Individual License for Commercial Use.

[nexpro]

I have visited the Pantheon several times over the years. It is truly astonishing.

[distant._.]

I love domes. I don’t have the Pantheon, but was able to build a wooden 3’ diameter rhombic triacontahedron to use as a “chandelier” in a modern built barn/shed.

Awesome content thank you for all of your efforts!

[harveysmith]

Can I make a small point to clear up any confusion. It was indicated when describing the concrete that cement was used to bind the materials together.
In Roman concrete, lime was used, not cement.

[thalesbastos]

Thank you for the info and dedication!

[JasonGerroll]

Linda, Paul - great video. Thank you for putting together.

[deborahlee]

Thank you Mr. Kassabian and Dr. Seymour for this great video! I just used it in my middle school engineering tech class connecting our lessons on materials, shapes, and forces. It was a perfect segway into their iconic structure research project.

[StereoSpace]

They made the walls thick. Exactly how thick they would have to work out. That's what fascinates me here. Did they build scale models, larger and larger, to see if the structural mechanics scaled up? I'm curious how they worked out what is sufficient to carry the loads.
They built domed baths too, so I wonder if they developed a formula that gave them a ratio of dome size to wall thickness, something practical/empirical like that.

[schoolofducttape]

Loved the form on this one! Breaking down one structure at a time is golden to me! I link to you whenever I make something structural, love the content! What are some abnormal building materials you find interesting?

[olgajoachimosmundsen]

Why does the hoop-forces transition from compression into tension? As a person with almost zero knowledge, but great interest in engineering I've watched most of your videos but struggle to really get the lesson home.

[scottcallow]

hi Paul, random question but one I can't seem to get an answer for. Theoretically what's the lowest vertical radius you can have with a dome using stone or concrete whilst it still is self-supporting and without framing? For a workable scenario, say a dome with a base equator diameter of 40m? thanks!!!

obviously I'm not an engineer, just curious :)

[MikeAG]

Imagine what they might have achieved if they had thought to rivet iron together to form a band all around the base of a dome.

[tururu]

I still don't get why is better to have the circle at the top for the structure😢