Carter Visits Arlington National Cemetery Defense Secretary Ash Carter leaves a challenge coin at the gravesite of Army Spc. Christopher David Horton at Arlington National Cemetery in Arlington, Va., May 22, 2015. Carter and his family members are friends with Horton's mother. Cemetery visitors often leave small rocks or personal markers on graves to let family members know they visited their loved ones. SHARE: Download: Full Size (0.08 MB) Credit: VIRIN: 905952-V-ATU57-420.jpg Photo Gallery