The Patterson Viaduct was built by the Baltimore and Ohio Railroad (B&O) as part of its Old Main Line during May to December 1829. The viaduct spanned the Patapsco River at Ilchester, Maryland. It was heavily damaged by a flood in 1868 and subsequently replaced with other structures. In 2006, it was restored to limited service when a footbridge was built atop the surviving arch and abutments.