Building The Cabin John Bridge

As late as the mid-19th century, Georgetown and Washington, D.C. lacked a plentiful and reliable source of safe drinking water and adequate water for fighting fires. In 1851 Congress commissioned studies to solve the city’s water problem well into the future. Lieutenant Montgomery C. Meigs of the U.S. Army conceived the plan for the Washington Aqueduct and supervised its construction. Completion of the aqueduct 12 years later allowed delivery of nearly 100 million gallons of water each day to the nation’s capital. An internationally renowned engineering accomplishment, the original aqueduct’s crowning achievement was the Cabin John Bridge, also known as the Union Arch Bridge, which has supplied drinking water to Washington since 1863. To transport materials to the bridge site, a dam was built on Cabin John Creek below the bridge location, and the resulting pool was connected by a lock to the C&O Canal, 1,000 feet to the south. Materials were loaded on canal barges at Georgetown or at the Seneca Quarry to the west and floated to a point beneath the bridge. A heavy timber trestle supported derricks and a traveling crane used to hoist timbers and stone into place, while a center arch of timbers supported the masonry during construction. The cut stone arch of Quincy granite, transported by ship from Massachusetts, was keyed on December 4, 1858. The centering structure was removed on August 12, 1861, when the spandrel arches were nearly completed and the maximum load was resting on the granite arch, which Meigs called the largest stone arch in the world, 220 feet in span.

Cabin John, Maryland · United States