Theodor Mommsen's History of Rome, for which he was awarded the Nobel Prize in 1902, was never completed. The manuscript of the fourth volume, the History of Rome under the Emperors, was burnt in a fire in Mommsen's house in 1880, and subsequently never published. Even though Mommsen lectured on the topic extensively from 1863 to 1886, it was believed that the lost volume could never be reconstructed. Alexander Demandt's discovery of complete and detailed transcripts by two of Mommsen's students finally gives us access to Mommsen's interpretation of the age of the emperors. Barbara and Alexander Demandt have carefully edited the text and provided detailed notes. For the English edition, Thomas Wiedemann has written an introduction which surveys Mommsen's position and influence in nineteenth century German scholarship and introduces his work to English-speaking readers.