A Crowded Chronology of Cities

For a change of pace, I've been working on a web page to illustrate the most populous urban areas throughout history: A Crowded Chronology of Cities

It's interesting that the graph of the population of the largest city isn't monotonic. As far as I can tell, there were two main "reduction" events:

• The fall of the Roman Empire
• The fourteenth century plagues (that's my guess, anyway!)