1,285 square kilometers

Photo from Wikimedia Commons
Rome (Metropolitan Area)
The Eternal City, capital of modern Italy and the ancient Roman Empire/Cities & Urban
Rome, the Eternal City, covers about 1,285 square kilometers as a municipality, making it the most extensive comune in Italy and one of the largest cities by area in Europe. The wider metropolitan area extends to about 5,352 square kilometers with a population of roughly 4.3 million. Founded traditionally in 753 BC, Rome served as the capital of an empire that controlled the entire Mediterranean world. The city contains an independent country (Vatican City, the smallest in the world at 0.44 km2) and an extraordinary concentration of ancient ruins, Renaissance churches, and Baroque fountains.
Measurements
5,352 square kilometers
Ancient city wall perimeter
3 lines, expanding slowly due to archaeology
Independent state within Rome
Average width through the city center