Since the first military burial on May 13, 1864, Arlington National Cemetery has become the final resting place for more than 400,000 soldiers, sailors, airmen, Marines and their families. Those who on Sept. 11, 2001, died only a few hundred yards away at the Pentagon are buried here, as are the Challenger astronauts. Fifteen thousand soldiers from the Civil War — Union and Confederate — rest in Section 27 and Section 13, known as the Field of the Dead. Four thousand freed slaves, many identified only as “Citizen,” and two presidents also are buried at Arlington. Section 60 is the…