And China had always many river systems which helped facilitate agriculture and trade. But as you get into the Sui Dynasty, right over here, you have the completion of the Grand Canal, which is even today the largest man-made canal. It stretches from Beijing to Hangzhou and actually goes beyond that and has other tributaries. And that, connected with the existing river systems, allowed for a lot of trade to happen, especially as we get into the Tang and the Song Dynasties. Now in the Song Dynasty in particular, you have the pound lock being invented, which allows for easier travel across waterways when you have a change in the level of water. And the pound lock is still the standard technology used in canals throughout the world. You also have the first use of paper money.