The marshy lowland area along the banks of the Tiber River was once considered suitable only for soggy military drills, until the Roman Empire conquered nature – along with the rest of Europe, parts of Africa and Britain – to build the first city of a million inhabitants in history. See how three millennia of transformation have turned such legendary sites as Piazza del Popolo, the Spanish Steps, the Pantheon, Piazza Navona, Campo de’ Fiori, Piazza Farnese and Michelangelo’s Piazza del Campidoglio into the historic centerpieces of a Modern European Capital.