I’ve been reading this weekend about the Monocacy Aqueduct, a bridge which carried the Chesapeake & Ohio Canal over the confluence of the Monocacy River and Potomac River. It was constructed between 1829 and 1833 and was one of “eleven stone aqueducts designed to carry the canal across the major river tributaries that drain into the Potomac River along the canal’s route.”  It spans 516 feet, has seven arches, and was constructed primarily of stone quarried from nearby Sugarloaf Mountain. 
Because the canal was used to carry war materials and men, Lee twice ordered it destroyed. The first directive was to General D. H. Hill who conducted preliminary raids into Maryland in early September, 1862. Hill was also to “disrupt the B&O Railroad.”  According to the Smithsonian Associates in an article here, lock keeper Thomas Walter, convinced Hill to drain the aqueduct rather than destroy it. While sympathetic to the Southern cause, Walter did not want to see the structure destroyed. 
Hill’s men cut banks holding out the Potomac River and put large boulders in the canal but all damage was largely repaired within two months.
More on the Monocacy Aqueduct later.
Interesting fact: The locks built on the Chesapeake and Ohio Canal were based on hydraulic designs by Leonardo da Vinci.
Because of the importance of waterways through the Civil War, I’ve renamed and expanded “the rivers” page on WigWags to “the waterways” page.
 “The Monocacy Aqueduct: An Icon of American Civil Engineering,” The National Park Service, http://www.nps.gov/archive/choh/History/Structures/Monocacy.html, access online August 2, 2009.
 nps.gov, http://www.nps.gov/choh/photosmultimedia/index.htm?eid=118223&root_aId=109#e_118223, accessed online August 2, 2009.
 Joseph L. Harsh, Take at the Flood: Robert E. Lee & Confederate Strategy in the Maryland Campaign of 1862, (Kent, Ohio: The Kent State University Press, 1999), 71.
 “The Monoacy Aqueduct,” The Smithsonian Associates, CivilWarStudies.org http://civilwarstudies.org/articles/Vol_5/monocacy.shtm, accessed online August 2, 2009.