Canal and River Structures

Lock 56 and lockhouse in the spring
Lock 56 and its associated lockhouse, near Hancock, MD.

Visitors to the C&O Canal NHP today can see many structures which were integral to the operation of the canal, including locks, lockhouses, aqueducts, bridges, culverts, feeder dams, and waste weirs. Even the canal is a historic structure - the canal itself is called the "prism," because the surface of the canal bed is wider than the bottom, making it prism-shaped. The prism was lined with clay to keep the water sealed inside.

Many of the structures which now remain are made of stone. The stonemasons were the most prominent craftsmen of the canal, painstakingly cutting blocks of stone to as small a tolerance as a half-inch. Today, the highway bridges that vault the river and the canal are formed of concrete, but this sort of construction did not develop until well after the canal was built. Concrete was not used on the canal until 1906, and is most commonly found as replacement work in waste weirs and lock pockets.

Paw Paw Tunnel
The Paw Paw Tunnel is an engineering masterpiece in western Maryland.

NPS Photo

One of the most iconic images of a C&O Canal structures is a lift lock, often called simply a lock. The 74 locks along the canal raised or lowered boats. Near most of the locks was a lockhouse which housed the lock keeper and his (or occasionally her!) family. Feeder dams were built on the Potomac River to supply water to the canal. Waste weirs, usually located near a dam, diverted excess canal water back to the Potomac River. Culverts protected the canal by diverting storm water runoff and local streams.

Only one tunnel was built on the canal, but that tunnel is a masterpiece of engineering. The Paw Paw Tunnel (mile 155) is 3118 feet long and constructed with over six million bricks!

Historic photo of Round Top Cement Company
The Round Top Cement Company provided quality cement for many years.  Some of the cement was  used on the C&O Canal.

NPS Photo

The Round Top Cement Company

The Round Top Cement Company was located at mile 127.4 of the canal. As land was being surveyed for the canal, investigators found a large outcrop of limestone along the river, on the downslope of a hill called Round Top. A Mr. Shafer immediately built a plant to turn the limestone into cement on what would become the berm side of the canal. A berm is generally a bank of earth; in this case, it is the side of the canal where the towpath does not run. The river provided water power until the canal was built, and then the plant used water from the canal. As of 1882, the plant employed 100 workers, and it could produce up to 2200 barrels of cement per week.

Last updated: April 30, 2020

Park footer

Contact Info

Mailing Address:

142 W. Potomac St.
Williamsport, MD 21795



Contact Us