Sgt. Robert Thornton Jr., 29, of Cairo, Georgia, was assigned to the 528th Sustainment Brigade. Thornton, a power generation equipment repairer, was running on Ardennes, which was closed to traffic for physical training, when he collapsed, a spokesman for the unit said. Several soldiers attempted to render aid and rushed Thornton to Womack Army Medical Center. The cause of death is unknown, officials said. His death is under investigation.