If we're going to use arbitrary points in time, at its peak Ancient Rome had over 1M inhabitants, and Chang'an had almost 2M, all before the IX century.
A more apt comparison might be London right before the car became common place, though.
The moment in time you pick for London does not change the picture. Victorian London still didn't have a million souls.
Rome's 1M population is a disputed number. Cities of tens of million inhabitants are all post-industrial and none work solely on mass transit. The car is an essential piece of the equation.
Car-less cities are an interesting thought experiment, but none has gone past the implementation barrier. That part of the equation should go into the though experiment.
> Victorian London still didn't have a million souls.
Can you provide a link? I'm either confused about what "Victorian" or "London" mean, because it seems to me that metro London definitely had over 1M people in the late 19th century.
A more apt comparison might be London right before the car became common place, though.