The Roman empire was antiquity’s largest and most powerful state. It reached its zenith under Trajan (r. 98–117), encompassing nearly 2 million square miles and containing some 60 million people. Linking its provinces were more than 250,000 miles of roads, 50,000 of which were paved. Roman engineers founded or improved more than 1,000 cities and towns, transforming the rural European landscape into a marvel of urbanization. In the third century the Roman army could field 450,000 infantry and cavalry and 45,000 sailors and marines. By the time Constantinople fell to the Ottoman Turks in 1453, the Roman army the oldest continually existing social institution in the Western world had been on the march for two millennia.
Rome itself was a magnificent example of cultural, technological and social superiority in its time. In 356 the city had 28 libraries, 10 basilicas, 11 public baths, two amphitheaters, three theaters, two circuses (the Circus Maximus could seat 150,000 people; the Colosseum, 50,000), 19 aqueducts, 11 public squares, 1,352 fountains and 46,602 apartment buildings. Yet little more than a century later barbarian invaders stood astride the empire’s corpse, the capital in ruins.