Factories arose with the introduction of machinery during the Industrial Revolution so they have been around for many years
In what years was the industrial revolution?
Somewere around the 1970s, Early factories that contained small amounts of machinery
1970s?  That doesn't seem right?  I thought it was back in the 1800s?  
It was 1760 sorry, And back then large factories tend to be located with access to multiple modes of transportation so many facilities under one roof.
Interesting.  Didn't they make a lot of pollution and smog?
Yeah back then laws were a lot more lax. Factories mostly make one kind of product and make it continuously.