The Thomas Viaduct was the first masonry arch bridge built on a curve and remains the largest of its type. Built by the Baltimore & Ohio it remains in use by B & O successor line CSX.
- Eight-span stone arch bridge over Patapsco River on the B&O Railroad between Relay and Elkridge
- Howard County, Maryland, and Baltimore County, Maryland
- Open to traffic
- Built 1835
- - Benjamin Henry Latrobe, Jr.
- Stone arch
Total length: 612.0 ft.
Posted to the National Register of Historic Places
- Approximate latitude, longitude
- +39.22192, -76.71317 (decimal degrees)
39°13'19" N, 76°42'47" W (degrees°minutes'seconds")
- Approximate UTM coordinates
- 18/352113/4342801 (zone/easting/northing)
- USGS topographic map
- Inventory numbers
- NRHP 66000388 (National Register of Historic Places reference number)
BH 42365 (Bridgehunter.com ID)
- September 26, 2012: New photos from Jann Mayer
- August 17, 2012: Updated by Daniel Hopkins: Added category "Railroad"
- October 2, 2010: Updated by Ed Hollowell: Added discription.
- April 19, 2009: Posted HAER photos
- HAER MD-3 - Baltimore & Ohio Railroad, Thomas Viaduct, Spanning Patapsco River, Elkridge, Howard County, MD
- Ed Hollowell - erhollowell [at] aol [dot] com
- Jann Mayer - jannmayer [at] gmail [dot] com