Click to enlargeNineteenth-century field fortifications or earthwork forts were constructed in various forms according to the topography of the land. They were constructed primarily from earth and wood, materials readily at hand, and were designed for temporary use. As this sketch illustrates, a framework was built, and as earth was removed from the "ditch" or dry moat that surrounded the fort, the earth was tamped (or rammed) into the framework. As the ditch grew deeper, the wall grew higher, extending to heights of 20-25 feet. The completed walls were 12-18 feet thick and were supported by a vertical pole system called "revetment."
Dennis Hart Mahan, professor of civil and military engineering at the U.S. Military Academy at West Point, New York, was primarily, if not solely, responsible for the theories of defensive warfare used by the Union and Confederacy during the American Civil War. Mahan taught the theories of military science developed in France by Marshal Prestre de Vauban, adapting Vauban’s principles to his own ideas of the changing nature of warfare. Mahan’s Complete Treatise of Field Fortifications (1836) and his Elementary Treatise of Advance-Guard, Outpost and Detachment Service of Troops (1847) were in use by army officers before the Civil War and became standard reference works for men who would lead armies for both the Union and Confederacy. Considered the nation’s leading military educator, Mahan would remain at the U.S. Military Academy during the Civil War as his theories were employed in every aspect of land warfare. Nowhere are Mahan’s theories on defensive warfare more visible than in General John G. Barnard’s design and construction of the Defenses of Washington.
