The Newkirk Viaduct Monument was designed by famous architect Thomas Ustick Walter in 1839 to celebrate the construction of the viaduct. The Newkirk Viaduct was the first permanent bridge at Grays Ferry (see photo below). The south side of the bridge had a track for the Philadelphia Wilmington & Baltimore Railroad, the north side was a roadway and the center span would telescope in and out to allow boats to pass on the Schuylkill. The bridge was named after the railroad's president and prominent Philadelphia businessman, Matthew Newkirk. The monument was moved here from its former site by the Amtrak Northeast Corridor and restored in 2016.
Bradley Peniston (via Hidden City Philadelphia) wrote a great article about the history of this viaduct and the monument. Read that article here.