In 1835, Maryland built a curved railway bridge from 63,000 tons of granite - critics thought it would collapse, but trains still cross it today

When engineers in the 1830s came up with the idea to build a big, curved railroad bridge across Maryland’s Patapsco River, a lot of people wondered if something so unusual could actually stand. At that time, most bridges were built using straight lines and well-known techniques, making it seem unlikely that a huge stone bridge with a big curve would hold. However, nearly two centuries later, the bridge is still there, and trains are still crossing over it. The American Society of Civil Engineers explains that the Thomas Viaduct was completed in 1835 using approximately 63,000 tons of granite, becoming one of the earliest major railroad bridges in the United States.

A bold solution for a growing railroad network

The United States experienced rapid growth of rail transportation during the early 1800s. As a result, there was a need for better and wider infrastructure. The Baltimore and Ohio Railroad, the first railroad in the country, required a bridge to carry trains over the Patapsco River Valley which could achieve the best possible route.


The challenge was the terrain. The solution came in the form of an arched bridge whose curvature corresponded with the terrain. Thus, the Thomas Viaduct was built and named in honor of the first President of the Baltimore and Ohio Railroad, Philip E. Thomas. The construction of the bridge was a bold venture since large stone bridges had not been built before in the United States.

A granite giant built to last

The bridge was composed of enormous quantities of granite. Around 63,000 tons of granite were used in the construction of the arches, piers, and structure of the bridge. The 8 stone arches spanned the valley in a gentle curve, which was both an elegant shape for a bridge and helped keep the railway on course.

Building a design like this in the 1830s was an incredible accomplishment. Workers transported and assembled thousands of granite blocks to construct the bridge, using advanced masonry engineering techniques available at the time. The defining characteristic of the bridge was the curvature. Many people doubted that the bridge would hold the weight of powerful trains, but the builders had faith in their creation. During construction, skeptics even nicknamed the project "Latrobe's Folly," reflecting widespread doubts that the curved granite bridge would succeed.

Proving the critics wrong

Finally, the doubts concerning the Thomas Viaduct were dispelled by the performance of the viaduct itself. Not only did it withstand the stress of trains crossing it, but it also kept operating despite the development of railroad technology and increasing weights of locomotives. Its survival demonstrated the importance of strong materials, thoughtful design, and careful construction. The viaduct has become an example of American engineers’ willingness to experiment with new approaches as the country’s transportation system developed.

At the same time, the fact that the bridge is still being used can be explained by the endurance of the infrastructure. While many structures from the 1800s have disappeared or required major replacement, the Thomas Viaduct remains an active part of the railway network.

A landmark connecting past and present

The Thomas Viaduct represents more than an old bridge. It marks a period when the United States was beginning to rely on railroads as a major force in economic growth and transportation. The Thomas Viaduct was designated a National Historic Landmark, recognizing its significance in American engineering and transportation history. Landmarks like this show how engineers solved complicated engineering tasks in the past with the tools and knowledge of that time.

Today, the bridge continues to serve its original purpose while also standing as a reminder of how infrastructure can outlast the expectations placed on it. The same granite blocks that once represented a risky experiment now form one of America’s longest-lasting railroad structures. The bridge remains in active railroad service nearly two centuries after its completion, demonstrating the durability of its original engineering and construction. On January 28, 1964, it was designated a National Historic Landmark, recognizing its importance in the development of American transportation engineering.

A bridge that shaped American preservation efforts

Beyond its role in railway history, the Thomas Viaduct also became an important example of how historic infrastructure can remain useful while being protected for future generations. This unique situation also makes the study of early 19th-century construction methods possible. Engaged in exploring the durability of materials and the maintenance requirements of structures like the Thomas Viaduct, engineers hope to find solutions that would allow older architecture to coexist with modern means of transportation.