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The Monocacy Aqueduct

The Smithsonian Associates Civil War E-Mail Newsletter, Volume 5, Number 7

Our founding fathers' goal to build a canal linking the Chesapeake Bay ports to the western territories of Ohio and beyond was the equivalent of our generation's goal to land on the moon. Like the space program, the vision for the C&O Canal was to facilitate travel, communication, and commerce between people and places. Unlike the space program, it fell far short of that vision.

What remains of this commercial failure is a civil engineering wonder: the Chesapeake and Ohio National Historic Park. The park consists of 74 canal locks, 11 stone aqueducts, 200 culverts, a half-mile-long tunnel cut through granite rock, and seven dams spanning 184.5 miles from Georgetown in Washington to Cumberland, Maryland. Although it operated for nearly 100 years and was the main source of coal, flour, and farm goods for the Capital, it eventually succumbed to the economics of cheaper and faster water and rail transportation. The most outstanding structure in the park is the Monocacy Aqueduct, built to carry the canal over the confluence of the Monocacy and Potomac Rivers.

The seven-arch aqueduct was completed in 1833 and is built of white and red quartzite, the same material used to construct the Smithsonian Castle. It spans 516 feet, with each arch at 54 feet. Approximately 300 workers were employed to haul materials and cut the stone. One hundred of the Irish immigrant stonecutters died during a cholera epidemic and are buried in a Roman Catholic churchyard in nearby Carrollton. Slaves also were employed, whose Maryland owners were paid eight cents per day for their labor.

During the Civil War the canal was used to transport war materials and troops along the border between Maryland, Virginia, and points west. For this reason the canal as well as the aqueducts were often under attack by the Confederates.

There were many Confederate sympathizers among the canal employees, including Thomas Walter, keeper of Lock 17. Walter loved the South, but he loved the Monocacy Aqueduct more. When he learned that Confederate General D. H. Hill had orders to destroy it in order to halt boat traffic, Walter convinced Hill that draining the canal would achieve the same end. Walter saved the Monocacy Aqueduct, only for it to be threatened once again a few months later.

At the onset of the Antietam Campaign in September of 1862, General Lee sent for General John G. Walker. Lee told him, "I wish you to return to the mouth of the Monocacy and effectually destroy the aqueduct."This was key to Lee's strategy to hold Harper's Ferry at the Confederate rear as they proceeded into Maryland.

Walker's men futilely attempted to drill holes and place gunpowder charges. He later wrote to Lee, "it was apparent that, owing to the insufficiency of our tools and the extraordinary solidity and massiveness of the masonry, the work we had undertaken was one of days instead of hours." To have continued "would leave my small division ... in a most exposed and dangerous position."Walker abandoned the plan and the aqueduct was spared once more.

But what the Confederates began Mother Nature nearly finished. The aqueduct was always subjected to weather, rain, and floods that took a toll on the stonework. From the Johnstown Flood in 1886, to Hurricane Agnes in 1972, to seasonal temperature variations, the structure continues to weaken.As early as 1937 a Historic American Buildings Survey (HABS) report stated, "The stones show signs of considerable movement and the stability of the arches is much impaired.It cannot be many years before the stones must fall and the aqueduct, with the action of frost and floods, begin rapidly to disappear."The HABS report graded the condition of the Monocacy Aqueduct as "Disintegrating."

Forty years after this death sentence, the devastation of Hurricane Agnes finally forced the government to act by installing braces to stabilize the structure and reduce further damage. In 1995, a tri-partnership of the National Park Service, the C&O Canal Association, and the National Capital Section of the American Society of Civil Engineers (NCS-ASCE) stepped in to monitor the stability of the structure and to develop a plan for restoration and repair. Recommendations notwithstanding, there was simply no money to do the work.

The turning point came in 1998, with great media fanfare, when the National Trust for Historic Preservation declared the Monocacy Aqueduct an endangered historic site. This encouraged Congress to appropriate $6.2 million to restore it, and the project is now underway. They won't use mules, slaves, or Irish stonecutters this time, but it will take more money and ingenuity to restore it than for our forefathers to build it.

Most of us will never get to the moon, but we can and should visit the Monocacy Aqueduct, just 42 miles upriver from Georgetown. We can appreciate it as the engineering marvel it was when it was built, as it still is considered today, and as it will be when it is restored and preserved for the future.