The historical centre ville is dominated by the traditional "Seven hills of Rome": the Capitoline, Palatine, Viminal, Quirinal, Esquiline, Caelian, and Aventine hills. The Tiber flows south through Rome, with the city centre located where the midstream Tiber Island facilitated crossing.
Large parts of the ancient city walls remain. The Servian Wall was built twelve years after Gauls' sack of the city in 390 BC; it contained most of the Esquiline and Caelian hills, as well as the whole of the other five. Rome grew out of the Servian Wall, but no more walls were constructed until 270 AD, when Aurelian began building the Aurelian Walls. These were almost twelve miles (19 km) long, and were still the walls the troops of the Kingdom of Italy had to breach to enter the city in 1870.
The old city center contains about 300 hotels and 300 pensioni, over 200 palaces, 900 churches, eight of Rome's major parks, the residence of the President of the Italian Republic, the houses of the Parliament, offices of the city and city government, and many monuments. The old city also contains thousands of workshops, offices, bars, and restaurants. Millions of tourists visit Rome annually, making it one of the most visited cities in the world.
