From The Daily Galaxy
"In 1000 A.D. Cordova, Spain was the largest city. By 1500, Bejing began its rise to power, and 300 years later it was the first city to be over a million people. By 1900 London emerged the world's supercity with over 6 million people. In 1950 New York was proclaimed the first "megacity" with a population of over 10 million people in the greater metropolitan area...
In 1950, there were 83 cities with populations exceeding one million; by 2007, this had risen to 468 urban areas of more than one million."
Interesting, but historic population sizes are tricky. I believe, for example, that Rome hit 1 million or more around 100 AD and may have peaked at 2 million. Various cities in China reached the 1 million mark at various times before 1500, including Bejing. But let's not allow facts to spoil a good story, even if this is fun facts to know and share. The last point is the most important because it is not the biggest city that matters, its the increasing and relentless urbanization of the human race.