The vantage point and lens setting compress distance but show how these bridges got their name. Bridging a river or stream is easiest at right angles, especially with cut stone. Outer portions of the S served to guide horse-drawn traffic and loose livestock. The curves were not a problem until the automobile era.

This original National Road bridge, beautifully restored, is from 1828 and open to pedestrians. US 40 traffic is just out of view in back.