Union Arch Bridge

Union Arch Bridge is a stone arch bridge in Cabin John that spans about 140 meters across the valley and carries both water from the Potomac River and vehicles on MacArthur Boulevard. The structure combines its role in the Washington Aqueduct system with accommodation for automobile and pedestrian traffic using protective barriers.

Construction occurred from 1857 to 1864 under Lieutenant Montgomery C. Meigs of the United States Army Corps of Engineers. The project arose from the need to create a strong crossing for the region's expanding water supply system during a period of significant national development.

The dedication plaques on the structure document political shifts during the American Civil War and show how its naming changed to reflect those turbulent times.

The location is easily accessible via MacArthur Boulevard, where both cars and pedestrians can use the crossing. It is worth viewing the structure and surrounding area from the valley below to fully appreciate the engineering achievement.

From 1864 to 1903, this held the record as the world's longest single-span masonry arch, marking a remarkable achievement in bridge engineering. This distinction reveals how advanced the technique was for building such a structure at that time.

Location: Montgomery County

Inception: 1857

Architects: Montgomery C. Meigs, United States Army Corps of Engineers

Length: 140 m

Made from material: granite, sandstone, dimension stone

Part of: Washington Aqueduct

GPS coordinates: 38.97290,-77.14800

Latest update: December 9, 2025 18:45