Relay, Maryland, Where the Horses Changed

The town got its name from a logistical problem. When the Baltimore and Ohio Railroad began operating in eighteen thirty as the first American passenger railway, horse-drawn cars made the run between Baltimore and Ellicott's Mills. The distance was too far for a single horse, so a fresh horse waited at the halfway point. That midway swap station became known simply as the relay.

The Thomas Viaduct followed, completed in July eighteen thirty-five: a six hundred twelve-foot curved stone bridge on eight semicircular arches, named for Philip Thomas, the B and O's first president. Built between July eighteen thirty-three and July eighteen thirty-five, it connected Relay to Elkridge and still carries rail traffic today, making it one of the oldest railroad bridges in continuous use anywhere in the world. What started as a horse-change stop became a footnote in railroad engineering history.