Neal Stephenson: They were entirely made up, but based on types that seem to have existed at that time. There was apparently a huge problem all over the place with what we would today call homeless people. They're called Vagabonds in the book. Sometimes there were more of them, and sometimes there were fewer of them, depending on what was going on in the way of wars or economic upheavals. There were encampments of people like this all over Christendom, as far as I can tell, and sometimes they would get together and rove around in big groups scaring the hell out of the citizenry.