Patterson Viaduct
The Patterson Viaduct, heavily damaged by a flood in 1866, spanned the Patapsco River at Ilchester, Maryland. Built from May to December 1829, the viaduct was part of the Old Main Line of the Baltimore and Ohio Railroad. It was constructed in the first building phase of the railroad, which extended from Baltimore, Maryland to Ellicott's Mills. The Patterson, the third bridge built for the Baltimore and Ohio, was similar in construction to the Carrollton Viaduct. Designed by Caspar Wever, it was built under the supervision of John McCartney, one of his assistants. McCartney received the contract to build the Thomas Viaduct as a result of his successful completion of the Patterson contract. The remains of the Patterson Viaduct stand on the east and west banks of the Patapsco River just south of the present railroad bridge. The bridge rose about 43 feet (13 m) above its foundations. It had four graduated arches " two of 55 feet chord (17 m) each and two of 20 feet (6 m) chord each. The smaller arches were introduced for the accommodation of two county roadways, one on each side of the river. The viaduct, constructed of granite blocks, was approximately 360 feet (110 m) in length. The exterior surfaces of the granite blocks were undressed, or rusticated. The viaduct was almost totally destroyed in an 1866 flood. A single-span Bollman Truss built into the west abutment in 1869 incorporated the original roadway arch and upstream wing wall. The Bollman design was supplanted by another bridge before the railroad was realigned about 400 feet (120 m) upstream in 1902”“1903 with the opening of the Illchester Tunnel. Today, all that remains at the original crossing is the single masonry roadway arch of the 1829 construction on the west bank and the stone abutment on the east bank. In 2006 a cable-stayed footbridge, with a design that echoes a Bollman Bridge, was added atop the abutments. The Patterson Viaduct Ruins were listed on the National Register of Historic Places on June 3, 1976.

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