What was the largest city in the world by the 1200s?

In the 1200s, the largest city in the world was Hangzhou, China with a population of about 1,000,000. However, other sources say that Baghdad, Iraq and Kaifeng, China were also the world's largest city with about 1,000,000 residents each as well. Another source lists Hangzhou as the largest city, but with a population of only 255,000.