The C&O Canal system has 12 aqueducts and 7 dams on the Potomac River. Back in the days when this canal was built, engineers did not know how to have a waterway such as a river or creek cross the canal, so they raised the canal above the waterways on an elevated structure like a bridge. These aqueducts are designed similarly to canal locks, but are larger and have no gates. Here is a reference on the C&O Canal Aqueducts: http://en.wikipedia.org/wiki/Aqueducts_on_the_C%26O_Canal
Here are a few examples:
The Monocacy Aqueduct crosses the Monocacy River where it meets the Potomac River, south of Nolands Ferry. Notice how much larger this span is than the others aqueducts shown here.
As a more unusual design detail, the end of the aqueduct wall forms steps which are both artistic and functional. The ends other aqueducts are simply buried in soil.
Near the Antietam National Battlefield is the Antietam Aqueduct. This aqueduct is also just a short distance north of Harpers Ferry National Historical Park, where you’ll find Locks 32 through 38 on the canal.
Notice the different color stone for the arches and the side walls of the aqueduct at Antietam Aqueduct. I’ll mention this more in further images.
Notice that the design of these following aqueducts is simpler than the earlier aqueducts which are closer to Washington DC. These were also built in later years, when labor and financial problems beset the Canal.
This aqueduct has been restored to its original appearance, but not all of the aqueducts I saw were in such good shape. Notice the arch portion is made of different colored stone from the side walls. Subsequent will show more about this design feature.
The far side wall of the Town Creek Aqueduct is missing.