Largest Cities in History by Peak Population

Data

Note: What We Know About History's Greatest Cities

The "million city" was rare before the modern era

Urban historians agree on a striking fact: for roughly 1,800 years, from Rome's peak around AD 1 to the dawn of the Industrial Revolution in the 1800s, only a tiny handful of cities worldwide ever reached a million inhabitants. Compare that with today, where more than 600 cities exceed a million people. This chart captures the elite pre-industrial club — the settlements that stood alone as the biggest places humans had ever built.

Why only a few cities could grow so large

• Food was the ceiling. Before railways and steamships, a city could only feed itself from the fields it could reach by cart or boat. Concentrating more than a few hundred thousand people meant commanding an enormous agricultural hinterland.
• Disease took a toll. Dense, unsanitary cities saw epidemic mortality constantly offset births. Rome and other megacities only stayed large by continuous in-migration from the countryside.
• Fuel scarcity. Heating and cooking ate up woodlands for miles around, and hauling firewood limited how big an urban centre could realistically get.
• Political power mattered. Every one of these giants was a capital or imperial centre that drew taxes, trade and tribute from a vast empire — Rome's grain fleet, Baghdad's caliphate, Chang'an's Tang empire.

The race for the first million

• Rome is widely credited as the first city to reach roughly one million people, around AD 1, as capital of an empire spanning the Mediterranean.
• Chang'an (modern Xi'an), capital of Tang China, hit about a million in the 8th century AD — arguably the world's most populous city of its day and a model of planned urban layout.
• Kaifeng, capital of the Northern Song dynasty, approached a million in the 11th–12th centuries, supported by a vast canal network feeding central China.
• The exact "first million" is debated because ancient censuses were not population counts, but Rome and Chang'an are the usual front-runners.

Who else was in the club

Beijing (Ming dynasty) and Constantinople (the Byzantine and Ottoman capital) hovered near or above 700,000, while Angkor in Cambodia — the heart of the Khmer Empire — grew to an enormous low-density city around 650,000 in the 13th century. The Indian subcontinent contributed Vijayanagar, and ancient China boasted Luoyang. It is worth noting that estimates vary from scholar to scholar: some put Baghdad's peak as high as a million around AD 900, and Tenochtitlan (modern Mexico City) likely neared 200,000–300,000 in 1520 as one of the largest cities on Earth outside Eurasia.

How historians estimate ancient populations

• Archaeology: excavating the area a city covered and dividing by an assumed density of people per hectare.
• Housing density: counting estimated dwellings within the walled area.
• Grain and tax records: using how much food or revenue a city consumed or produced as a proxy for people.
• Census fragments: Roman, Han and Song censuses give some numbers, though they counted households or taxpayers rather than total residents.
• The result is a range of estimates — different scholars can disagree by 20–50% on the same city, so treat all figures as well-grounded estimates rather than exact counts.

Fun facts about the ancient megacities

• Rome at its peak needed a dedicated fleet of ships to haul grain from Egypt and North Africa just to feed its million residents — the "annona" system.
• Tang Chang'an was designed as a perfect grid with 108 walled wards, a plan that influenced the layout of Kyoto and other East Asian capitals.
• Angkor was a "hydraulic city" — a sprawling low-density metropolis organised around a vast network of reservoirs and canals, bigger by land area than many medieval European capitals.
• Kaifeng's growth rode on the Grand Canal, which let a single city feed off the surplus of the whole Yangtze delta.
• The Industrial Revolution broke the ceiling: London passed a million around 1810, and by 1900 dozens of cities had done the same — the ancient million-city club became unremarkable.
• Today the largest cities, like Tokyo, exceed 37 million people — more than 30 times the scale of ancient Rome.