This is a kilo of tortillas. That’s what one person in a city needed. It’s the same weight, more or less, whatever the grain is—you can go to the historical record, you can research in China, in India, in the Near East, and you will still be talking about 2 lbs of grain-based food for every person in the city every day.
So you can do some calculations. If you’ve got a city of a million, like ancient Rome, you’ve got to get two million pounds of grain into the city every day. It’s the same for all the cities in the world— it’s 2 lbs of grain per person. That’s the power, that’s the energy that drives cities.
This is a pretty cool article on the evolution of food production in Mexico and the way in which mass production of tortillas and wheat breads is transforming Mexican society.