Many canals connect two bodies of water that lie at different elevations. Locks are used to gradually move the ships from one elevation to another. Once a ship enters a lock, doors close in front of and behind it. Water is then added or drained from the area to raise or lower the ship to a different elevation. Then the doors in front of the ship open and the ship sails down the canal to the next lock or to the open sea.
The Panama Canal is a remarkable achievement in engineering. Completed in 1914 and costing the lives of over 27,000 workers, the canal cuts shipping routes in half.