The canal itself was a "prism", wider at the water's surface than at the bottom, and large enough for two boats to pass each other. Digging and blasting the channel for the canal was hard and dangerous work, and the result was often just referred to as a ditch. The masonry parts were held in higher esteem, and were termed "works of art" in the canal company's documents. These included the locks, culverts, aqueducts, and the waste weirs that regulated the flow of water through the canal and turned it into an engine to lift and lower the canal boats.

The stonemasons were the most prominent craftsmen of the canal, painstakingly cutting blocks of stone to as small a tolerance as a half-inch. Unfortunately, this sort of craftsmanship is much too time consuming and expensive for the modern world. The highway bridges that vault the river and the canal are more sensibly 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. 

Some C&O Canal structures are:

Lift locks - raised or lowered boats much like an elevator

Lock houses - located next to locks; the lock keeper and his family lived inside with the lock keeper operating the lock as needed

Feeder Dams - built on the Potomac River, they supplied water to the canal

Waste weirs - diverted excess canal water back to the Potomac River, usually located near a dam

Culverts - diverted excess canal water under the towpath

The Paw Paw Tunnel - the only tunnel built on the canal