Originally posted by wildWolverine
Worker Housing is absolutely incredible in terms of production, you have no way of cleaning up the resultant pollution (not sure how a boarding house creates pollution?!?)... This made me realize that some kind of advance is necessary to clean up the pollution -- I just never realized it, because by the time I normally have pollution (i.e., factories, coal plants, etc.), I must have already researched that advance. What is the advance necessary to clean up pollution?
edit: or is this just a quirk of the Mesopotamia conquest?