They come back with paper and paper money. Europeans are still like lugging around gold and stuff like that. They come back with compasses, which is going to be huge in terms of map making. And, of course, they come back to a big perin. No, of course not. They come back to what you always come back to Europe in the 13th century, which is war. Marco Polo is captured and in prison he starts telling his tales, which gets put into the Book of Marvels, The Travels of Marco Polo.