The conquistadors wrote that the cities they encountered in present-day Mexico were often larger, grander, and more densely populated than the cities of Europe they were used to. Why were the Aztecs and their neighbors able to out-build Europeans to such an extent?
Listen to Podcast Episode #33, starring /u/400-rabbits.
EDIT: I do not believe any of the podcast episodes have been transcribed, so I look forward to reading a detailed text answer as well if someone is willing.
EDIT2: /u/Cozijo has previously answered Why were Natives of South and Central America always so incredibly ahead of their neighbours in North America?