The photograph shows a reflection of the abutment on the Maryland side of the New Armory Dam, constructed between 1859-61 to supply water power to the national armory at Harpers Ferry on the West Virginia shore (originally the State of Virginia). Adjacent to the Chesapeake & Ohio Canal and constructed from grey limestone with rough facing, the structure was intended to improve on – and ultimately replace – Dam #3 (visible in the map below, also known as the 'Government Dam'). The latter, built in 1799 over the Potomac river, supplied both the armory and the Chesapeake & Ohio Canal with water.
The national armory at Harpers Ferry was first established in 1802. Between 1844 and 1854, extensive expansion of the buildings and machinery had necessitated the need for more water power. The armory canal was enlarged and seven new water turbines were installed. With the destruction of the armory during the Civil War, the dam was never completed.