The Atlantic Monthly | March 2002

"Before it became the New World, the Western Hemisphere was vastly more populous and sophisticated than has been thought—an altogether more salubrious place to live at the time than, say, Europe. New evidence of both the extent of the population and its agricultural advancement leads to a remarkable conjecture: the Amazon rain forest may be largely a human artifact.(and, Tim writes, perhaps the agro-forests and "gardens" along the eastern coast as well, illustrated by the many stone constructions we've been talking about.)Maize, as corn is called in the rest of the world, was a triumph with global implications. Indians developed an extraordinary number of maize varieties for different growing conditions, which meant that the crop could and did spread throughout the planet...
Indian agriculture long sustained some of the world's largest cities. The Aztec capital of Tenochtitlán dazzled Hernán Cortés in 1519; it was bigger than Paris, Europe's greatest metropolis. 
From the article that became the book "1491"by Charles C. Mann

Whole Text: http://cogweb.ucla.edu/Chumash/Population.html