How ancient metropolises managed populations of one million people

Historians and archaeologists have reconstructed the layout of antiquity's largest metropolises using indirect estimation methods. Since official population censuses from these eras are lost, researchers calculate population density by analyzing the length of city walls, building foundations, urban footprints, food supply logistics, and the size of necropolises. The Scale of Power: Rome and Chang'an Chang'an, the capital of China's Han and Tang dynasties, stood as one of the most influential centers of the ancient world. By the 1st and 2nd centuries AD, its population may have reached one million people. The city followed a strict grid system, organizing palaces, markets, and residential quarters into a precise order. Its position at the eastern terminus of the Great Silk Road transformed it into a critical hub for trade and intellectual exchange between China, Central Asia, and India. Rome mirrored this scale, with its population approaching one million during the early imperial period. Under the Pax Romana, the city became a laboratory for infrastructure, deploying extensive aqueduct systems, public baths, and amphitheatres. Rome remained Europe's largest urban center until its decline in the 5th century AD.