History's Greatest Mysteries

As one of the greatest military leaders in history, his conquests were so legendary that some believed he was descended from the gods. At only 32, with a vast empire that was rapidly expanding, Alexander the Great died unexpectedly.

In the final days of the Civil War, Confederate leaders fled south, rumored to be carrying the Confederate treasury worth an estimated $13 million in today's money. But when Jefferson Davis is captured, there's no treasure in his baggage.

As the country reels in the aftermath of 9/11, an entirely new threat spread across the nation. Deadly anthrax spores sent through the mail kill five people and spread authorities thin.

On Sept. 11, 2001, coordinated terrorist attacks change America; mastermind Osama bin Laden threatens further violence, prompting a global manhunt by U.S. intelligence forces; nearly a decade later, U.S. Navy SEALs raid a compound in Abbottabad, Pakistan and kill him during a night operation.