The Longest Stone Arch Bridge In America
Pennsylvania's Rockville Bridge is the longest stone masonry arch bridge (viaduct) in America and the world. It crosses the Susquehanna River, stretching 3,820 feet (1,164 meters) across the water in forty-eight 70-foot spans. The bridge is used by the Norfolk Southern Railroad and Amtrak and links Harrisburg with the west shore of the river. It was built between 1900 and 1902 by the Pennsylvania Railroad and included four tracks until two were removed.
Deciding The Longest Stone Arch Bridge
The Rockville Bridge fulfills several criteria to take the top ranking. In this article, the longest stone arch bridge is defined as a continuous rail or vehicular viaduct (still in use). The criteria also include arches and piers that bear the load. The viaduct is measured from abutment to abutment to determine its total length. If the definition changes to the longest single-span stone arch, the Casselman Bridge in Maryland can vie for the top spot.
Building A Bridge To Last Forever
Before the Rockville Bridge was constructed, another bridge stood in its spot. The bridge was used by the Pennsylvania Railroad and later, the Northern Central Railway. A second bridge replaced the original wooden structure with a double-track iron truss bridge. This bridge became overwhelmed by too-heavy locomotives.
It took two years to build the Rockville Bridge, and the project was one of William Henry Brown's best achievements. Brown was the chief engineer of the Pennsylvania Railroad, and under his leadership, 800 workers (including hundreds of Italian laborers) constructed the bridge using 220,000 tons of stone. Brown was the one who pushed for stone construction over iron and wood, and he also ensured that more stone-arch bridges were constructed (around two to three a year).
The bridge carried four main line tracks for nearly 100 years before they were reduced to three during the 1980s. In the late 1990s, an accident that saw an intermodal container blown off an intermodal freight train prompted the removal of yet another main line. The bridge still operates using two main line tracks. It also survived two floods and was protected by armed guards during both World Wars. This has earned the bridge the title of 'the bridge built to last forever.'
Crossing The Rockville Bridge
The Rockville Bridge is used by trains only. Norfolk Southern Railway operates freight trains over it, while Amtrak runs a passenger service. Amtrak's Pennsylvanian train crosses the bridge daily as it carries passengers between New York City and Pittsburgh.
In July 2026, the Union Pacific Big Boy No. 4014 traveled across the bridge from Dauphin County to Perry County to celebrate America's 250th birthday. People joined watch parties to view the more than one-million-pound train make its way over the bridge. The event saw the largest operating steam train in the world crossing the longest stone arch bridge.
More Historic Stone Arch Bridges
Some of America's other stone arch bridges also deserve a mention, especially when looking at different categories and criteria. The 2,100-foot (640-meter) Stone Arch Bridge in Minneapolis, built in 1883 across the Mississippi River, features 23 stone arches. It is the only stone arch bridge spanning the river and is also the second-oldest stone arch bridge on the river. Unlike the Rockville Bridge, the Stone Arch Bridge is no longer in rail service. Today, it is used only as a pedestrian and bicycle path.
Connecticut's Bulkeley Bridge was completed in 1908, and it still stretches across the Connecticut River. The bridge has nine arches and is 1,192 feet (363 meters) long. It is considered the longest stone arch bridge constructed for highway traffic and carries Interstate 84, U.S. Route 6, and U.S. Route 44.
Pennsylvania has another claim to stone bridge fame in the Starrucca Viaduct. The bridge opened in 1848 and contains 17 stone arches. It is one of the oldest active stone rail bridges in North America, but at a length of 1,040 feet (317 meters), it is far shorter than the Rockville Bridge.
Maryland has three notable bridges, namely the Thomas Viaduct in Relay, the Casselman Bridge in Grantsville, and the Cabin John Bridge/Washington Aqueduct Bridge in Montgomery County. The Thomas Viaduct Railroad Bridge is 612 feet (187 meters) long, features 8 arches, and was opened in 1835. It is the oldest stone rail bridge that still carries heavy freight traffic and the world's largest multiple-arched stone railroad bridge built on an arc.
The Casselman Bridge was constructed between 1813 and 1819, and it was the longest single-span stone bridge in the U.S. when it opened (80 feet). Finally, the Cabin John Bridge (Union Arch Bridge) held the world record for the longest single stone span for almost 40 years. When it was completed in 1864, its arch was 220 feet (67 meters) long.
The Heyday Of Stone Bridges
The golden era of building major stone arch railroad bridges did not last long. Stone arch bridge projects were propelled by the growth of 19th-century transportation. Before the mid-1800s, most American roads relied on short stone arches or wooden bridges to cross streams. When steam trains replaced wagons, wooden bridges became too dangerous. Iron bridges were not much better, since they could not handle the vibrations of freight trains. They also experienced structural failures.
Stone bridges offered a permanent solution. Stone blocks lock under compression. An arch transfers downward weight outward into stone piers and riverbed foundations. As such, American railroads invested in stone arch bridges between the 1830s and early 1900s. Stonemasons and laborers built massive river crossings all over the country, including the bridges in Maryland, Pennsylvania, and Minnesota.
Yet, the stone bridge heyday was already winding down when the Rockville Bridge opened. Hand-fitting sandstone blocks took too much time and money. And the process could not compete with the new developments in concrete and structural steel. By the 1910s, engineers largely abandoned most stone masonry projects in favor of new materials.
Built To Last
When the Rockville Bridge was built, the idea was that it would stand forever. Considering all it had to withstand, that idea does not seem too unrealistic. The bridge still carries freight trains across Pennsylvania after more than 120 years. And it might just outlast some of the most modern bridges built today.
