Suspension bridges are spectacular for spanning long distances. But the classic design of swooping cables, high towers, and a suspended roadway is practical as well as breathtaking.

The cables are subject to a stretching force called tension. They transfer some of the bridge's suspended weight into the rock-solid anchorages at either end.

The towers are subject to a pressing force called compression. The cables transfer some of the bridge's weight onto the towers, which push down into their bedrock foundations.

Bridge designers calculate compression and tension so that bridges will stand under their own weight.