Stop 1 · Italy
Rome
The first city known to reach a million people, around the 2nd century AD. By 500 AD it had collapsed to perhaps 30,000.
Cities that were once the largest on earth
The title has moved around for three thousand years. Each of today's stops held it — one of them still does.
The five stops
Stop 2 · Iraq
Baghdad
It was probably the first city since Rome to pass a million people, around 900 AD, and the largest in the world for roughly two centuries.
Stop 3 · China
Nanjing
Probably the largest city in the world around 1400, with something like 500,000 people inside those walls.
Stop 4 · United Kingdom
London
The largest city in the world from about 1825 to 1925 — the first to pass five million, and the first to pass eight.
Stop 5 · Japan
Tokyo
It has held the title since roughly 1955 and has never come close to losing it. The metropolitan area alone would be the world's 20th-largest economy.
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Think you'd have found them? Play today's expedition, or replay this one from the archive.