The episode covered, stone arch bridges, some are still in service and outlasted iron bridges. The one arch Carrolton Viaduct (1829) is the oldest in the U.S., and the 8 arch Thomas Viaduct (1835) just west of Baltimore is the next oldest. The Rockville Bridge over the Susquehanna 1902 replaced earlier wooden (1849) and iron (1879) bridges. Tunkhannock Viaduct/Nicholson Bridge 2,300 feet length, 240 feet above the community of Nicholson, PA., built in 1915 was given as the ultimate example.