The Ponakin Bridge is a historic Post truss bridge in Lancaster, Massachusetts. The bridge was built in 1871, and originally carried the main north-south road (now Ponakin Road), which was bypassed by the construction of Massachusetts Route 70. It is now unsafe and closed even to pedestrians.
The bridge trusses consist of eight paneled sections with a total span of 100 feet (30 m) and a width of 20 feet (6.1 m). It rests on granite stone abutments. The decking consists of a base of cross timbers which are attached to the trusses, with wood stringers, then transverse cross timbers, and finally three inch deck planking.