UNESCO designated the “Historic Center of Rome” a World Heritage Site in 1980, declaring the area inside the Aurelian Walls (plus Vatican City, just outside the walls) as the city's Centro Storico. Many consider the smaller area covering what was once the ancient Campus Martius (now the location of the Campo Marzio rione, or quarter) as the true Centro Storico, however. Regardless of how you measure it, the Centro Storico, home to the Pantheon, Temple of Hadrian, the Basilica of Santa Maria sopra Minerva, Piazza Navona, and Campo de' Fiori, is one of the most important neighborhoods in the Eternal City. The Trevi Fountain, Roman Forum and Colosseum, and Piazza di Spagna and the Spanish Steps are just outside the narrowest interpretation of the Centro Storico, as is Vatican City across the Tiber River.
Because of its narrow streets and pedestrian-only areas, the best way to visit the Centro Storico is on a walking or electric-bike tour that includes Rome’s most important sights. Many Ancient Rome tours also cover some or part of the Centro Storico, as do night tours.