Block House #4, ca. 1905.

Block House #4 sat on the massive glacial rock outcropping at 123rd Street and Amsterdam Avenue. It was one of a series of stone defense fortifications constructed around the War of 1812. Despite the preparation for the perceived threat of British invasion, the British never made it to Manhattan during the war. The ruins of Block House #4 remained on the outcropping until the 1960s when Public School 36 was constructed on the site. The sections of the school where built directly on the large rock, which can still be seen on the 123rd Street side.

A single block house survives in the northern section of Central Park; it is also situated on a large rock outcropping.