But as trade became more important, especially as you go through Central Asia, you could imagine that many of the people who were very good at trading, who were good at moving things, were people who were good at moving themselves, in particular, the nomadic people in Central Asia. Many of their cities along these trade routes became more and more wealthy and more and more powerful. Now, as I mentioned, goods were not the only thing that were transported along these routes. One of the not-so-good things was the spread of disease. So in the historical record, we have two major plagues in Rome during the Roman Empire, and we believe these plagues were smallpox, although some people believe it might have been measles. And it is believed that it came from traders, it came from Asia, from the Middle East, and these were significant plagues. And the reason why we think that it was due to trade is that there's some evidence in Han China during this first plague of similar symptoms, of a similar plague.