Dunlap's Creek Bridge is the first arch bridge in the United States built of cast iron. It was designed by Richard Delafield and built by the United States Army Corps of Engineers. Constructed from 1836 to 1839 on the National Road in Brownsville, Pennsylvania, it remains in use today. It is listed on the National Register of Historic Places and is a National Historic Civil Engineering Landmark (1978). It is located in the Brownsville Commercial Historic District and supports Market Street, the local main thoroughfare. Due to the steep sides of the Monongahela River valley, there is only room for two short streets parallel to the river's shore and graded mild enough to be comfortable to walk before the terrain rises too steeply for business traffic.