This bridge was built in the heart of the colonial era, about 16 years after William Penn had been granted the land for granted the land for the Pennsylvania Colony by King Charles II, and the idea of a United States was not even a thought at the time. The colonists who built this bridge could never have imagined that their bridge would endure for over 300 years, into the 21st Century, and carry motorized traffic... a traffic type that the colonists could not have imagined in their wildest dreams.
The bridge has been significantly altered over its period of history, as one might expect of a bridge built over 300 years ago in the colonial era that today continues to carry vehicular traffic at an impressive 20 ton weight limit. The most significant alteration was that the bridge was widened by adding a stone arch to the south side of the bridge in 1893. This 1893 arch follows the shape and design of the original 1697 structure and today this "new" part of the bridge is well over 100 years old and historic in its own right. The other major alteration is the 20th Century addition of a concrete ring to the inside of the 1697 arch. Other alterations include the deck replacements and the addition of a cantilevered sidewalk. Finally, the bridge's stonework has been repaired numerous times over its history, although most of these repairs have been carried out in-kind and were respective to the original materials and craftsmanship of the bridge. Despite all these alterations, the bridge continues to convey the design of the 1697 structure and on the 1697 half of the bridge continues to display a significant amount of original bridge material.
Even with the alterations present on the bridge, the sheer age of this bridge and its association with the colonial history of the Americas (one of only a few surviving bridges with this distinction) make this bridge one of the most significant in the United States.
An article with a reference to and picture of the bridge: