Chambered locks area a common feature on canals around the world. The first one, however, was located on the Grand Canal in China, dating back to 983 A.D. A lock is a mechanism for moving a boat or ship up or down an elevated portion of a river. The boat enters the first chamber of the lock, which is sealed by watertight gates at either end. The water level then rises or falls to the level of the second chamber, depending on the direction the boat is trying to go: upriver, the  chamber fills; downriver, the chamber empties. Once the desired level is reached, the gate in front of the boat opens and the process is repeated. Below is an image of a modern lock from the lower elevation.

Locks on the Ottowa River, from The New York Times, at nytimes.com.

Building the World Blog by Kathleen Lusk Brooke and Zoe G. Quinn is licensed under aCreative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.