andromeda:
<
The first people to settle into villages apparently gave little thought to
what to do with their trash, so they just lived in it -- until they couldn't
take it anymore.

http://www.world-science.net/exclusives/040923_trashfrm.htm
...
By the later Neolithic, "you have really big villages, even double-story stone houses, and
up to thousands of people living in single village," Edwards said. "It'll become fairly
obvious to them after a while that epidemics will spread rapidly through lack of
sanitation, sewage and so on. They'll get pretty aware that 'we can't live like this
anymore.'"
>

London caught on to this in the 18th century, iirc.