C&O Canal National Historical Park
21115 Mouth of Monocacy Road
Monocacy Aqueduct While hiking the picturesque 184.5-mile C&O Canal Trail, one will come across eleven stone aqueducts originally designed to carry the canal across several of the Potomac River's tributaries. Completed in 1833, this 516-foot limestone aqueduct with seven arches spanning 54 feet, is the canal's largest intact structure. It's a civil engineering marvel that has withstood Civil War, hurricanes, and floods.