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Canal boats being pulled up hill on the Allegheny Portage Railroad, circa 1845.
Credit: Courtesy Pennsylvania Historical and Museum Commission
While working on the Pennsylvania Main Line of Public Works, Roebling witnessed first-hand the perils of the Allegheny Portage Railroad's use of hemp rope to haul barges from the canal up the steep inclines of the Allegheny Mountains. Too often, the hemp snapped, sending barges on a free-fall down the mountainside. The replacement of hemp with Roebling's wire rope marked the beginning of a revolution in American engineering.