In 401 B.C., a thundering army of mercenaries, camp followers, dreamers, and glory seekers set off to help a rebellious foreign general named Cyrus. In the months that followed, ten thousand men--trained and hardened in three decades of war in Greece--would engage in pitched battles, witness untold horrors, and begin a desperate march across he desert, over raging rivers, and into the jaws of hell itself. By the time it was over, some would be alive,...