Marker relates that a nearby ruin is Fort Montgomery, named for Revolutionary War General Richard Montgomery, killed at Quebec in 1775. Construction was begun in 1844, and guns were removed in 1900.
There is considerably more to the story here. The fort itself is listed on the National Register of Historic Places, but visiting it is out. It is private property, not to mention structurally unsound. It can be seen easily from a fishing access parking lot on the Vermont side of the US Route 2 bridge. There is also an interesting YouTube video.