Baltimore and Ohio Railroad at Relay, Maryland
A section of the Baltimore and Ohio Railroad (B&O) in Relay, Maryland. The B&O was the first passenger railway in the United States, debuting in 1830 with 13 miles of track between Baltimore City and Ellicott's Mills (later Ellicott City) with trains originally drawn by horses. The distance between the two endpoints was too long for a single horse to complete, so a new horse known as a "relay" waited at the halfway point of the trip. This halfway point developed into the town eventually known as Relay, as it was the spot where the horses were exchanged. The left set of tracks go over the Patapsco River via the Thomas Viaduct, and visible at left is the obelisk built on the Relay side of the bridge to commemorate the viaduct's construction.