Thomas Viaduct

Thomas Viaduct is a stone railroad bridge spanning the Patapsco River with eight granite arches in a curved design between Relay and Elkridge. The structure continues to carry freight trains and MARC Camden Line commuter trains today.

The Baltimore and Ohio Railroad built this stone bridge between 1833 and 1835, creating the first multi-span masonry railway bridge in the United States. This structure marked a turning point in American railroad infrastructure.

An obelisk at the eastern end displays the names of railroad directors, engineers, and builders who created this structure. These inscriptions preserve the memory of the people behind this engineering achievement.

The viaduct is best viewed from nearby roads where visitors can see the arches and overall structure clearly. Morning or late afternoon light works well for photographs of the stone surfaces.

The structure survived the great flood of 1868 and Hurricane Agnes in 1972 with barely a scratch, while most surrounding buildings in the Patapsco Valley were destroyed. This resilience showed that the stone arch construction was exceptionally sound.

Location: Baltimore County

Location: Howard County

Inception: 1835

Made from material: stone

GPS coordinates: 39.22170,-76.71330

Latest update: December 7, 2025 20:46