The Rockville Bridge: A Million Tons of Stone
Near Harrisburg, Pennsylvania
About two miles north of the city, the Susquehanna River is crossed by something that takes a moment to properly register. The Rockville Bridge is the longest stone masonry arch railroad viaduct ever built anywhere on earth. It stretches three thousand eight hundred twenty feet, nearly three-quarters of a mile, on forty-eight individual arches, each spanning seventy feet. It required two hundred twenty thousand tons of stone and six hundred thousand barrels of cement. At peak construction, nearly three hundred stone masons worked the site simultaneously.
The Pennsylvania Railroad built the Rockville Bridge between nineteen hundred and nineteen oh two, as the cornerstone of an ambitious program to replace every wooden and iron bridge in its system with stone and concrete. The idea was permanence. Wood rots and iron corrodes, but stone, properly laid, theoretically lasts forever. The Pennsylvania Railroad wanted infrastructure that would outlast not just the current generation of trains, but any foreseeable generation.
They were not wrong. The bridge was designed to carry the heaviest freight loads of the early twentieth century, but it has handled locomotives and freight cars far heavier than its engineers could have imagined. It still carries active rail traffic today, operated by Norfolk Southern and Amtrak, more than a hundred and twenty years after it opened.
In flood years, and the Susquehanna has produced some devastating floods, the Rockville Bridge has stood. Record-setting floods in nineteen thirty-six and nineteen seventy-two both swept beneath it without structural consequence.
It was named a National Historic Landmark in part because it solved a problem once thought to require iron or steel, and solved it so permanently that it has never needed a successor.
