The Keystone Arch Bridge in New Salem, Massachusetts, stands as a remarkable testament to both engineering ingenuity and historical significance. Located just north of the Quabbin Reservoir, this bridge spans the middle branch of the Swift River and is widely recognized as one of the state's most unique and beautiful bridges. The Keystone Arch Bridge was constructed in 1866 by an intriguing figure named Adolphus Porter.

Adolphus Porter's life story adds an interesting layer to the history of the bridge. Before taking on the monumental task of building this bridge, Porter had a military background. He served in the military and was wounded at the battle of New Bern on the outer shore of North Carolina. Following his injury, he was sent home and granted a pension. However, Porter chose an unconventional path by relinquishing his pension, reenlisting, and serving until the end of the war. A relative of Porter's mentioned that Adolphus lost one of his legs during the Siege of Petersburg.

Upon his return to Massachusetts, Adolphus Porter embarked on the ambitious project of constructing the Keystone Arch Bridge. While Porter had the flexibility to build various types of bridges, he chose to construct one of the most challenging varieties—an arch bridge without the use of mortar, frequently referred to as a mortarless arch bridge. Instead of using mortar to fill gaps and provide structural integrity, Porter meticulously positioned each stone so that they could support the bridge without the need for mortar by leaning against eachother. Among the most challenging stones to secure were the top capping stones, as they carried minimal weight and were vulnerable to impact from bridge use. Porter's solution was to use large stones for added stability.

The exact duration of the bridge's construction is unknown, but it is reasonable to estimate that it took several months or even a few years. Adolphus Porter relied on basic hand tools and had no access to modern equipment, making the great structural integrity of this bridge even more remarkable. Upon completing the bridge, it served the purpose of allowing Orange-Millington Road to cross the river, providing a great transportation link for the area.

Over time, Orange-Millington Road was closed and transformed into a recreational path. The state subsequently acquired ownership of the bridge and the surrounding land. In an effort to ensure the bridge's functionality and enhance safety for users, a concrete slab was added to the bridge deck. This modification has contributed to the bridge's continued utility and safety.

For those interested in visiting the Keystone Arch Bridge, it is easily accessible from Quabbin Gate 30, located on Route 122. Visitors can conveniently park alongside Route 122 in front of the gate and embark on a short 100-yard walk to reach the bridge. The trail leading to the bridge is well-suited for walking, running, and biking, offering a pleasant outdoor experience. While the bridge's history might not be immediately apparent to all visitors, the remarkable story behind the Keystone Arch Bridge in New Salem, Massachusetts, adds an extra layer of fascination to this extraordinary structure.