Since the great flood of 1927 killed hundreds of people, the Army Corps of Engineers has built 2000 miles of levees to tame the Mississippi. Now the system's being tested as never before, as the Corps is faced with opening spillways to devastate some places in order to save others. At stake either way are homes, businesses, billions in property damage and entire communities. Is the River untamable after all? We hear from the Corps and its critics and from the Mayor of Vicksburg, Mississippi, one city that's bracing for a catastrophe.