The Colosseum: the jewel of Ancient Rome. It wowed vast crowds with extraordinary battles. It pushed the boundaries of technology. It exhibited Rome's vast wealth and power. Roman leaders spread the Colosseum's design throughout the Empire, and it helped them conquer the ancient world. But just as the structure embodied Rome's power, so too did it contribute to the Empire's downfall.

Just below the Mediterranean's surface, in Alexandria's harbor, lay the ruins of a mysterious ancient monument. For more than 20 years, French explorer Franck Goddio has been hoping to confirm these remains are a temple belonging to Cleopatra. If true, this discovery could reveal vital new information about Cleopatra's reign and her connection with the goddess Isis.

In early 2003, three amateur codebreakers announced they had successfully decoded the secret correspondence of one of the most tragic characters in European history: Mary, Queen of Scots. 57 encrypted letters detail the exiled queen's efforts to free herself from imprisonment and gain advantage over her rival, Queen Elizabeth. Now, after four centuries, Mary's urgent pleas can be revealed.

Follow scientists as they track down the earliest known bubonic plague victims in hopes of preventing future outbreaks, while historians and scholars explore the societal impact of the plague on medieval Europe. What happens when a third of a continent’s population is wiped out?