I remember from a trip to Italy a few years ago that Roman cemeteries were always located on the outskirts of which ever city the were supplied from. If I remember correctly the dead essentially had a city of their own. What is the reason for this practice? I remember when I visited Ostia Antica that the cemetery was basically at the entrance to the port city. Was this the case for all roman cemeteries? Were there any other caveats involved in the locations of cemeteries?
Pollution! In Roman religious practice, there is an idea of pollution and purity. There was nothing more polluting than death. In fact, there was an extreme purifying ritual to be done after a death in the house. Pollution was extremely bad in Roman religion. It was a major crime to step into a sacred space when polluted. The cemeteries were set outside the city boundaries to prevent the city from becoming polluted. Actually, the first werewolf stories recorded come from people walking through these roman cemeteries.