Pantheon with an Archaeologist: How the Wall Actually Carries the Dome

This tour is pitched at people who want the technical answer, and the archaeologist leading it gives one. The building has three names and three lives. Santa Maria ad Martyres, the basilica consecrated to the martyrs. The Pantheon, the imperial statement of what Rome could build. And the temple raised on the site by Agrippa under Augustus, later rebuilt on Hadrian's instruction into what stands now. It still holds the remains of men and women who shaped Italian culture and politics. The part most visitors never get told concerns the wall. What looks like a solid ring of masonry is nothing of the kind: it is a system of piers, voids and relieving arches, and the weight of the dome does not press evenly on it but travels down through those piers to the ground. Seen that way, the wall stops being a wall and becomes a piece of structural reasoning, which is harder to photograph and much harder to forget.