For the Roman Empire to survive? I've been thinking on a alt plot-line, but it's rather obsure. I'm getting a lot the information about the period from Historical Fiction, specifically three books/book series. Breen's "Eagle in the Snow" , Poul Anderson's "the King of Ys", and Jack Whyte's "Camulod Chronicles". I was just reading Eagle in the Snow, and it was talking about the Germanic Tribes crossing the Rhine, and I was thinking "what could stop them?" And then I got an idea... What if they were hit by diseases? Enough so that the couldn't overcome Roman resistance. I had in mind not a totally healthy surviving Roman Empire, but the tribes really coming to terms with the Romans, and peoples like the Romanized Gauls Britons and other people having their own states. One group that kept coming up was the Vandals. I wanted to get rid of them, since they did nothing worthwhile. But what happended to the Marcomanni, and the Quadi?