5 votes

CSX - Thomas Viaduct


Aerial View Looking Southeast

Photo taken by Historic American Engineering Record

View photos at Library of Congress

BH Photo #137334

Street Views 


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
Elkridge, Howard County, Maryland, and Baltimore County, Maryland
Open to traffic
Built 1835
- Benjamin Henry Latrobe II of Philadelphia, Pennsylvania (Designer)
- Baltimore & Ohio Railroad (BO)
- CSX Railroad (CSX)
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)
Quadrangle map:
Inventory numbers
NRHP 66000388 (National Register of Historic Places reference number)
BH 42365 (Bridgehunter.com ID)

Update Log 

  • October 16, 2016: New photo from Dave King
  • March 17, 2016: New photo from Luke
  • April 16, 2015: New photos from David McCardell
  • September 29, 2014: New photos from Alexander D. Mitchell IV
  • May 26, 2014: Updated by Luke Harden: Added cities
  • 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
  • Wikipedia
  • Jann Mayer - jannmayer [at] gmail [dot] com
  • Luke
  • Alexander D. Mitchell IV
  • David McCardell - mccardelldavid [at] gmail [dot] com
  • Dave King - DKinghawkfan [at] hotmail [dot] com


CSX - Thomas Viaduct
Posted September 22, 2022, by GH (golociusa [at] netscape [dot] net)

The bridge structure is historically in the earlier archives known as the "Thomas Viaduct at Relay":

*https://archive.org/details/TheThomasViaductAtRelayMaryland (1921)

* 1996 ICOMOS.org "Context for World Heritage Bridges", Author Eric DeLony, noted preservationist & chief of the Historic American Engineering Record (HAER, 1971 - 2003)

* Figure 13 Thomas Viaduct (1835), Relay, Maryland (USA). This illustration is from The United States Illustrated (1850).Smithsonian Institution

* https://www.youtube.com/watch?v=0HUQZMtOoHk

* History of Relay, Maryland, and the Thomas Viaduct (1995), Author Daniel Carroll Toomey

* https://whatsupmag.com/culture/relay-maryland-s-historic-hor...