Roman History, Volume IV

Dio Cassius (Cassius Dio), ca. 150–235 CE, was born at Nicaea in Bithynia in Asia Minor. On the death of his father, the Roman governor of Cilicia, he went to Rome in 180, entered the Senate, and served as an advocate under the emperor Commodus. He held high offices and became a close friend of several emperors. He was appointed governor of Pergamum and Smyrna, served as consul in 220, and was proconsul of Africa. He later became governor of Dalmatia, then of Pannonia, and served as consul again in 229.

Of the eighty books of Dio's great work, Roman History, which covers the era from the legendary landing of Aeneas in Italy to the reign of Alexander Severus (222–235 CE), we possess Books 36–60 (with gaps in 36 and 55–60), which cover the years 68 BCE–47 CE. The missing portions are partly supplied by Zonaras, who relies closely on Dio, and for some later gaps (from Book 35 onwards) by John Xiphilinus, from the eleventh century. Additionally, there are many excerpts available. The facilities for research provided by Dio's official duties, along with his personal diligence, make him a critical source for understanding the Roman history of the last years of the republic and the first four emperors.

The Loeb Classical Library edition of Dio Cassius is published in nine volumes.