Today's Blue Line was once a very short subway
going from Bowdoin in downtown Boston only three stations to Maverick in East Boston.
The route under the Harbor
utilized a converted streetcar tunnel that dated back to the earliest years of last century.
modified for subway use in the early 1920s.
The outdoor extensions didn't take place until after World War II, and were built
in large part along former narrow-gauge railroad right of way. Structures
such as this overpass obviously go back to long before the "T"
was running here.