Historians tell us that by the very end of the Roman Empire, goods were pouring into Rome from all over the known world, but about the only thing being sent out of Rome was human waste and garbage.
http://theeconomiccollapseblog.com/...s-export-to-china-waste-paper-and-scrap-metal
http://theeconomiccollapseblog.com/...s-export-to-china-waste-paper-and-scrap-metal