This curved granite viaduct with eight arches was built in 1835. Incredibly it is still being used... with modern heavy trains on the double tracks! Designed by Benjamin Henry Latrobe, Jr. (1806-78), the son of the architect of the US Capitol and Baltimore's Basilica, it was 612 feet long and cost over $142,000 or the equivalent of $3.8 million. At the time it was called Latrobe's Folly, since it was so novel detractors thought it would fall down.
The following site has a FABULOUS animation of how the Thomas Viaduct was built. HERE
A second website has great historic photographs, including one showing two trains crossing at the same time! HERE
Morse sent his famous 1844 telegraph message "What hath God wrought?" from the Capitol to Baltimore over the Thomas Viaduct, post HERE
Builder's monument and the Thomas Viaduct.
The first "mealing station" at Relay by the Thomas Viaduct HERE