Located in north-central China, Chang'an was the capital of more than 10 dynasties. It became the largest city in the world under the Sui Dynasty as China emerged as the world's most powerful country.

Soon the city sprawled across more than 30 square miles, and by 700 it had a population of 1 million.

The poet Bai Juyi said the city had "hundreds of, thousands of houses — like a great chessboard … like a huge field planted with rows of cabbages." It had tree-lined boulevards five times as wide as New York's Fifth Avenue.

Chang'an declined sharply at the end of the Tang dynasty in 904. It lives on today, however, as the booming city of Xi'an.