Our ability to have transactions in our society are not dependent on our ability to mine for gold or silver or copper. And one of the things that allowed for paper money to even be used was this notion of block printing and block printing with movable type in particular. Once again, a Song Dynasty innovation. Now as I mentioned, as we get into 1127, you have conquerors from the north, in particular the Jin, who are able to conquer northern China. They caused the Song to move their capital from Kaifeng in the north to Hangzhou in the south. Here you see Hangzhou is the major southern terminal of the Grand Canal. And even though the northern Song had to move and essentially become the southern Song Dynasty, you continue to have that prosperity for roughly another 150 years.