Dion Cassius Cocceianus, a historian of Rome, born in Nicaea, Bithynia, about A. D. 155, went to Rome about 180, where he was made senator. He was afterward appointed to many offices of trust by different emperors, and was twice consul. Having become odious to the praetorian guards, because, it is said, of his severe discipline, he obtained permission from the emperor Alexander Severus, in 229, to retire to his native city, where he spent the remainder of his days. His great work was a history of Rome written in Greek, divided into 80 books, and containing an account of the rise and progress of the state from the landing of AEneas in Italy until A. D. 229, giving only a slight sketch of events down to the time of Julius Caesar, but dwelling with minuteness on the history of later times, and especially on that of the author's own age. Of this work, which is written with clearness, diligence, and general accuracy, but in a faulty style, 19 books (from the 36th to the 54th) remain entire. Fragments of the first 35 have been collected, and there are abridgments of the last 26, as well as of the entire work.

One of the best editions is that of Sturz (9 vols. 8vo, Leipsic, 1824-'43). An English translation of Xiphilin's abridgment was published in London in 1704.