History & Heritage

Thomas Viaduct Railroad Bridge

ASCE National Historic Civil Engineering Landmark

The Thomas Viaduct Railroad Bridge in Relay Maryland has been designated as a National Historic Landmark by the American Society of Civil Engineers (ASCE).

The Viaduct was the most challenging part of the first railroad line to the U.S. Capital city. When

opened in July 1835, it was the longest stone arch bridge in the world. The viaduct is one of unusual size for its time. To add to the problems of designing and constructing such a massive viaduct, site conditions required that it be located on a curve. Its overall length of 614 feet is divided into eight arches with an average span of 58 feet and a total height of 60 feet above mean sea level. The chief design problem arose from the construction on a curve, causing variations in span and pier width between opposite sides of the structure. The lateral; pier faces were set on radial lines, for which Latrobe found few, if any, precedents.

The ASCE Maryland Section, is working to have a bronze plaque mounted near the viaduct to honor the designation. The plaque will be cast to look similar to the photo below and include the following wording:

NATIONAL HISTORIC

CIVIL ENGINEERING LANDMARK


THOMAS VIADUCT, MARYLAND

One of the earliest curved railroad viaducts in the United States. This eight-arch masonry structure required an innovative design to support the lateral loads and construction challenges because of the curvature. The viaduct was designed by Civil Engineer Benjamin Henry Latrobe, Jr. (1806-1878) and constructed by the Baltimore & Ohio Railroad. The viaduct was a critical link for the first rail line into Washington, DC and it continues to carry much heavier rail traffic.

CONSTRUCTED: 1835

ESIGNATED: 2010

Plaque Location

We plan to mount the plaque on a boulder (similar to adjacent photo). We have located a boulder of the same granite that was used to construct the viaduct at the Woodstock Quarry. The plaque & boulder will be placed near the contact station along the Park Entrance Road in the Avalon Area of Patapsco State Park. The plaque will be placed in the landscaped beds, just behind two other markers, one of which is about the Viaduct. Our plaque will add context and significance to the viaduct by noting its historical and engineering significance. The location will be visible to all who visit the park.

Project Schedule

The Maryland Section of the American Society of Civil Engineers is sponsoring this project. We are raising funds for the pedestal, mounting of the plaque, retention of a contractor, and for delivery. We expect that we will schedule and conduct an unveiling ceremony after the plaque is installed sometime in 2023. We are encouraging the local ASCE members, and railroad organizations, companies, and individuals to join us as we permanently honor and designate the Thomas Viaduct. We are soliciting funds to pay for:

  • Casting the plaque

  • Hauling the stone

  • Mounting the plaque to the stone

  • Placing the stone at the Park Site

  • Costs for the unveiling

Our fundraising goal is $3,500 to cover these expenses. Please consider a donation to help make the plaque a reality! We also invite your suggestions and participation as we plan the ceremony. All organizations that provide donations will be displayed and invited to the ceremony.

Contact Information

We welcome the opportunity to discuss this in more detail, please contact:


Ken Derrenbacher kderren@schnabel-eng.com

William Parks waparkssandp@gmail.com

Mike O’Conner mike@fplmuseum.org

Donation Information

Please submit your donation no later than February 28, 2023. ASCE is a 501 (c) 3 organization, so your donation may be tax deductible.

Thank you for your consideration of this effort to honor the Thomas Viaduct.