Historian Tom Holland has adapted Homer, Herodotus, Thucydides and Virgil for BBC Radio. His other history books include Rubicon, Persian Fire and The Forge of Christendom. Sadie Holland / hide caption

itoggle caption Sadie Holland /

A U.S. Army honor guard stands at attention during a ceremony to mark Memorial Day, this week at Arlington National Cemetery. Mandel Ngan/AFP/Getty Images hide caption

itoggle caption Mandel Ngan/AFP/Getty Images