Lucius Cassius Dio (; c. 155 – c. 235 AD)[note 1] or Dio Cassius (Ancient Greek: Δίων Κάσσιος Dion Kassios)[note 3] was a Roman statesman and historian of Greek and Roman origin. He published 80 volumes of the history on ancient Rome, beginning with the arrival of Aeneas in Italy. The volumes documented the subsequent founding of Rome (753 BC), the formation of the Republic (509 BC), and the creation of the Empire (27 BC), up until 229 AD. Written in Ancient Greek over 22 years, Dio's work covers approximately 1,000 years of history. Many of his 80 books have survived intact, or as fragments, providing modern scholars with a detailed perspective on Roman history.
Lucius Cassius Dio was the son of Cassius Apronianus, a Roman senator and member of the gens Cassia, who was born and raised at Nicaea in Bithynia. Byzantine tradition maintains that Dio's mother was the daughter or sister of the Greek orator and philosopher, Dio Chrysostom; however, this relationship has been disputed. Lucius is often identified as Dio's praenomen, but a Macedonian inscription, published in 1970, reveals the abbreviation, "Cl.", presumably Claudius.[note 4] Although Dio was a Roman citizen, he wrote in Greek. Dio always maintained a love for his hometown of Nicaea, calling it "his home", as opposed to his description of his villa in Italy ("my residence in Italy").
For the greater part of his life, Dio was a member of the public service. He was a senator under Commodus and governor of Smyrna following the death of Septimius Severus; he became a suffect consul in approximately the year 205. Dio was also proconsul in Africa and Pannonia. Severus Alexander held Dio in the highest esteem and reappointed him to the position of consul, even though his caustic nature irritated the Praetorian Guards, who demanded his life. Following his second consulship, while in his later years, Dio returned to his native country, where he eventually died.
Dio published a Roman History (Ῥωμαϊκὴ Ἱστορία, Historia Romana), in 80 books, after twenty-two years of research and labour. The books cover a period of approximately 1,400 years, beginning with the tales from Roman mythology of the arrival of the legendary Aeneas in Italy (c. 1200 BC) and the founding of Rome by his descendant Romulus (753 BC); as well as the historic events of the republican and imperial eras through 229 AD. The work is one of only three written Roman sources that document the British revolt of AD 60–61 led by Boudica and the subsequent defeat of Boudica. Until the first century BC, Dio provides only a summary of events; after that period, his accounts become more detailed. From the time of Commodus (ruled AD 180–192), Dio is very circumspect in his conveyance of the events that he witnessed.
The version of Dio's work that survives today is quite composite since his history does not survive in its entirety: The first 21 books have been partially reconstructed based on fragments from other works as well as the epitome of Zonaras who used Dio's Roman History as a main source. Scholarship on this part of Dio's work is scarce but the importance of the Early Republic and Regal period to Dio's overall work has recently been underlined. Books 22 through 35 are sparsely covered by fragments. The books that follow, Books 36 through 54, are nearly all complete; they cover the period from 65 BC to 12 BC, or from the eastern campaign of Pompey and the death of Mithridates to the death of Marcus Vipsanius Agrippa. Book 55 contains a considerable gap, while Books 56 through 60 (which cover the period from AD 9 through 54) are complete and contain events from the defeat of Varus in Germany to the death of Claudius. Of the 20 subsequent books in the series, there remain only fragments and the meager abridgement of John Xiphilinus, a monk from the 11th century. The abridgment of Xiphilinus, as now extant, commences with Book 35 and continues to the end of Book 80: it is a very indifferent performance and was made by order of the emperor Michael VII Doukas. The last book covers the period from 222 to 229 (the first half of the reign of Alexander Severus). Dio's work has often been deprecated as unreliable and lacking any overall political aim. Recently, however, this Roman historian has received a thorough reevaluation and his complexity and sophisticated political and historical interpretations have been highlighted.
The fragments of the first 36 books, as they have been collected, consist of four kinds:
Dio attempted to emulate Thucydides in his writing style. Dio's style, where there appears to be no corruption of the text, is generally clear though full of Latinisms. Dio's writing was underpinned by a set of personal circumstances whereby he was able to observe significant events of the Empire in the first person, or had direct contact with the key figures who were involved.