Concrete is the most widely used man-made material in the world. It is hidden under the surface of the city: forming the foundations of skyscrapers, snaking underground as tunnels, retaining tons of earth laterally to clear space for inhabitation, or anchoring the steel structure of the elevated train lines. New York is, after all, the concrete jungle.

In the opening decades of the 20th Century, the proliferation of new subway lines in Brooklyn changed the shape of Brooklyn's busiest intersections; new routes were excavated and transit hubs born, replacing the streetcars and elevated railways of years past. This collection includes a selection of photographs documenting subway construction in and around Times Plaza, Flatbush Avenue, and Ashland Place.

Worker posing with a siphon form during construction on the BMT Fourth Avenue line, near 13th Street, July 2, 1915. The 8'5" wooden scaffold was used for pouring concrete.