Clark's Ferry Bridge was part of the Main Line Pennsylvania Canal built in 1828. Mules walked on a cantilevered walkway outside the structure and towed canal boats across the river. The dam below the bridge, known as Green's Dam, created a calm surface for the canal boats. The bridge ended the hand-poled ferry that had existed at this location for nearly 50 years. Seven different bridges have crossed the Susquehanna here. Although in Dauphin County, the bridge always had a strong connection to Duncannon and contributed greatly to its growth in the mid-1800s. The covered bridge that once stood in the distance was considered at the time to be the longest covered bridge in the world at 2088 feet.