Being a student of real history, the plague was used as an offensive weapon of war in real battle, so it would be obvious that they would use it to poison the food and water supply of their opponents in secret. They were all doing it, kind of like spying on your friends and enemies today via tech. Using the excuse that no one knew how to clean out the Roman sewers is bs and unimaginative; otherwise it would have occurred much sooner. Not saying those things didn't stink, though. Btw, good digit catch.