Museo dell'Ara Pacis Crypt (Mausoleo di Augusto)

The recently reopened tomb of Augustus and the entire Julio-Claudian dynasty — Augustus, Tiberius, Caligula, Claudius, Nero. The original 87m-diameter circular structure was the largest tomb in the ancient world. After centuries of decay and use as everything from a fortress to a concert hall, it reopened in 2021 after a 14-year restoration.