Set in a very modern glass building, which you can walk around for free, and surrounded by more historic structures, the white marble “Altar of Peace” was created in 9 b.c. to honor the achievements of (soon to be Emperor) Augustus in subduing tribes north of Alps. It was later lost to memory and though signs of its existence were discovered in the 16th century, it wasn’t until the 1930s that the ancient monument was fully excavated. After World War II it lay virtually abandoned until the 1970s. But true restoration only began in the 1980s, and the current building, finished in 2006 to a design by American architect Richard Meier, is one of the most poignant showcases of Imperial Rome.

The onsite museum provides context, with interactive displays in English and Italian. Note that you get great views of the huge, overgrown ruin of Augustus’s Mausoleum (Mausoleo di Augusto) from here, but the 1st-century b.c. tomb itself—where the ashes of emperors Augustus, Caligula, Claudius, Nerva, and Tiberius were once stored—is closed to the public.