Rome's most famous physical features are the Tiber River and the seven hills upon which the city is built. These are Aventine Hill, Caelian Hill, Capitoline Hill, Esquiline Hill, Palatine Hill, Quirinal Hill and Viminal Hill.
The Centro Storico (Historic Center in English) lies at the heart of Rome and contains famous sites such as the Campo dei Fiori, Colosseum, Piazza Navona, Pantheon, Roman Forum, Spanish Steps, Trastevere and the Vatican. This area is the oldest part of Rome and has been almost continuously inhabited for the past 2000 years.
However, the city has grown greatly since then. While the entire city was contained within the Servian Wall in the early 4th century BC, it later expanded so much that the Emperor Aurelian built a second wall stretching 12 miles in 270 AD to protect the capital. Today, the city has expanded past the walls once again. The Tiber River was the only major body of water that touched the original Roman settlement, but the city today touches the Tyrrhenian Sea, which is some 15 miles east of the Centro Storico, and the Aniene River now falls within its borders.
The city of Rome is part of the larger Commune of Rome, which includes 496 square miles of land. Much of this area is marshland, causing the commune to have a much lower population density than the city of Rome itself.