In this segment of Secrets of Underground London, learn about the secrets of London's past, all hidden underneath the city. The ruins of a Roman amphitheater, which held 6,000 people, was found under the Guildhall Art Gallery. Additionally, under the Museum of London has thousands of human bones preserved under its foundation, revealing the history of London through its inhabitants. Victims of the Black Plague, who were found in plague pits, can be found in the archive. Scientists have been able to track down the cause of the horrific, unstoppable plague by examining these centuries-old bones.