Since the beginning of time (or nearly so) mankind has been gathering in big groups. Most of the time these big gatherings are "cities" or "towns". As these places mature so does their infrastructure, providing the residents with some of the things we need to survive, including shelter, access to food, heat, protection from others, a place to sell our goods and services, a place to engage in a trade, water, sanitation, etc.
Many times very large numbers of people have gathered without a city being present. The way this Bear sees it, here are some examples:
Major battles, involving tens of thousands of participants.
Tent cities, lately in Africa, with refugees pouring in, making these places huge.
Some of these places have millions of people, often with little or no services.
Huge rock concerts, such as Woodstock and Goose Lake. (Bear was at GL.)
Woodstock was nearly a half million people. Goose Lake was 400,000.
Some of the world's larger soccer stadiums hold hundreds of thousands of fans.
The Indianapolis 500.......isn't that about a quarter-million fans?
University of Michigan's football stadium......over 110,000 every football Saturday.
Any other examples?
Three Days, Man....Three Days....Lotta Freaks Bear