The Fort Ward Museum and Historic Site in Alexandria, Virginia in the Washington DC area is worth visiting. The defenses of Washington during the Civil War were Vauban-type earthworks located on the high ground outside the city -- the engineer officer who designed the fortifications also had to incorporate some of the hasty positions dug in 1861 before a proper terrain analysis had been done. My Dad took my brother and I to Fort Ward in 1959 when archeologists employed by Alexandria were excavating the site in preparation for turning it into a park. At about the same time a few hundred yards from the fort where I then lived a girl found a .69-caliber spherical musket ball while we kids were playing with toy cars in the dirt.