Tacitus Primary Source: Probably the greatest writer of history in the Latin language. The Annals and Histories cover the period from the death of Augustus (AD 14) to the Batavian Revolt (AD 70), although neither have survived intact. He also wrote a biography of his father-in-law Agricola, detailing his campaigns in Britain, and the Germania, a description of the Germanic peoples. Tacitus is well-known for his dry, sarcastic sense of humour and clear disdain for the imperial system that had replaced the old republic. His books are a must-read for anyone interested in the history of the early imperial period. There is a good Penguin edition of both the Agricola and Germania in a single volume, and the Penguin translations of both the Annals and Histories are also good.

• https://www.amazon.co.uk/Agricola-Germania-Penguin-Classics-Tacitus/dp/014045540X/ref=sr_1_2?keywords=tacitus&qid=1567159801&s=gateway&sr=8-2
• https://www.amazon.co.uk/Annals-Imperial-Rome-Classics/dp/0140440607/ref=sr_1_3?keywords=tacitus&qid=1567159861&s=gateway&sr=8-3

Suetonius Primary Source: A biographer rather than a historian, Suetonius wrote accounts of the lives of the first twelve Caesars, from Julius Caesar to Domitian. Suetonius is sometimes dismissed as a gossip and rumour-monger, and it’s true that his biographies often contain the kinds of sordid details that, in the modern world, we’d expect from celebrity tabloids. However, this shouldn’t distract from the serious scholarly work that he put into researching and writing these accounts. Without them our knowledge of the actions and personalities of the early emperors would be much poorer, and indeed once Suetonius runs out we miss him.

Cassius Dio Primary Source: a historian, writing in Greek, who lived under the Severan dynasty at the end of the second/beginning of the third century. His monumental work covers Roman history from its foundation to his own time, although large sections are now either lost or survive only in summaries written in later periods.

Plutarch Primary Source: Plutarch is most famous for his Parallel Lives, a series of paired and broadly moralizing biographies of eminent Greeks and Romans. But with only two exceptions (the emperors Galba and Otho) the subjects of Plutarch’s biographies lived before the imperial era. Much more useful for the historian of imperial Rome are the disparate treatises collectively known as the Moralia, which paint a splendid picture of the world and worldview of an educated Greek living in the Pax Romana.