Urban+decay~filth+in+the+city

Were the structures of the buildings in Rome causing them to crumble and decay? If so, what type of structures were poor and cause the decay?
 * Question on urban decay**

Are there any architectural/ construction techniques that can be used while designing and constructing a building, that would help prevent the decaying of the building or even postpone the on set of decay ? Have theses techniques been tested to confirm their effectiveness on the decaying of buildings?