The work on dreams and prodigies, which we mentioned above, is lost. Dion had probably written it only to please the emperor, and he seems afterwards to have regretted its publication; for, although he is otherwise rather credulous and fond of relating prodigies, yet in his history he mentions those which have reference to Septimius Severus only very cursorily.

He afterwards incorporated this in his history of Rome.

This work is mentioned only by Suidas; and, if it really was a distinct work, the substance of it was incorporated in his Roman history.

is likewise mentioned only by Suidas, but is probably a mistake, and Suidas confounds Dion with Deinon, who is known to have written a work on Persia.

Ἐνόδια, that is, , is mentioned by Suidas ; but it is very doubtful whether it was a work of Dio Cassius, or of his grandfather, Dion Chrysostomus, whose extensive travels may have led him to write such a work.

A is altogether unknown, except through the mention of Suidas.

is attributed to Dio Cassius by Suidas, Jornandes, and Freculphus; while from Philostratus (Vit. Soph. 1.7) we might infer, that Dion Chrysostomus was its author.

(Ῥωμαικὴ ἱστορία), the great work of Dio Cassius, consisted of 80 books, and was further divided into decads, like Livy's Roman history. It embraced the whole history of Rome from the earliest times, that is, from the landing of Aeneas in Italy down to A. D. 229, the year in which Dion quitted Italy and returned to Nicaea. The excerpta, which A. Mai has published from a Vatican MS., and which belonged to a work containing the history from the time of Valerian down to the time of Constantine the Great, bear indeed the name of Dio Cassius, but are in all probability taken from the work of a Christian writer, who continued the work of Dion, and A. Mai is inclined to think that this continuation was the work of Joannes Antiochenus. Dio Cassius himself (72.18) intimates, that he treated the history of republican Rome briefly, but that he endeavoured to give a more minute and detailed account of those events of which he had himself been an eyewitness. Unfortunately, only a comparatively small portion of this work has come down to us entire. Of the first thirtyfour books we possess only fragments, and the Excerpta, which Ursinus Valesius, and A. Mai have successively published from the collections made by the command of Constantine Porphyrogenitus. A few more fragments have recently been published by F. Haase (Dionis Cassii librorum deperditorum Fragmenta, Bonn, 1840, 8vo.), who found them in a Paris MS. It must further be observed, that Zonaras, in his Annals, chiefly, though not solely, followed the authority of Dio Cassius, so that, to some extent, his Annals may be regarded as an epitome of Dio Cassius. There is a considerable fragment commonly considered as a part of the 35th book, which however more probably belongs to the 36th, and from this book onward to the 54th the work is extant complete, and embraces the history from the wars of Lucullus and Cn. Pompey against Mithridates, down to the death of Agrippa, B. C. 10. The subsequent books, from 55 to 60, have not come to us in their original form, for there are several passages quoted from these books which are not now to be found in them; and we therefore have in all probability only an abridment made by some one either before or after the time of Xiphilinus. From book 61 to 80 we have only the abridgment made by Xiphilinus in the eleventh century, and some other epitomes which were probably made by the same person who epitomized the portion front the 55th to the 60th book. A considerable fragment of the 71st book was found by A. Mai in a Latin translation in the Vatican library, of which a German version was published anonymously Braunschweig, 1832, 8vo,); but its genuineness is not quite established. Another important fragment of the 75th book was discovered by J. Morelli, and printed first at Bassano, and afterwards (1800) at Paris, in folio, uniform with Reimarus's edition of Dio Cassius.

Notwithstanding these great losses, we possess a sufficient portion of the work to enable us to form a correct estimate of its value. It contains an abundance of materials for the later history of the republic and for a considerable period of the empire, for some portions of which it is our only source of information. In the first of the fragments published by A. Mai, Dion distinctly states, that he had read nearly everything which had been written on the history of Rome, and that he did not, like a mere compiler, put together what he found in other writers, but that he weighed his authorities, and exercised his judgment in selecting what he thought fit for a place in his work. This assertion of the author himself is perfectly justified by the nature and character of his history , for it is manifest everywhere that he had acquired a thorough knowledge of his subject, and that his notions of Roman life and Roman institutions were far more correct than those of some of his predecessors, such as Dionysius of Halicarnassus. Whenever he is led into error, it is generally owing to his not having access to authentic sources, and to his being obliged to satisfy himself with secondary ones. It must also be borne in mind, as Dion himself observes (53.19), that the history of the empire presented much more difficulties to the historian than that of the republic. In those parts in which he relates contemporary events, his work forms a sort of medium between real history and mere memoirs of the emperors. His object was to give a record as complete and as accurate as possible of all the important events; but his work is not on that account a dry chronological catalogue of events, for he endeavours, like Thucydides, Polybius, and Tacitus, to trace the events to their causes, and to make us see the motives of men's actions. In his endeavours to make us see the connexions of occurrences he sometimes even neglects the chronological order, like his great models. But with all these excellences, Dio Cassius is the equal neither of Thucydides nor of Tacitus, though we may admit that his faults are to a great extent rather those of his age than of his individual character as an historian. He had been trained in the schools of the rhetoricians, and the consequences of it are visible in his history, which is not free from a rhetorical tinge, especially in the speeches which are introduced in it. They may not be pure inventions, and may have an historical groundwork, but their form is rhetorical; though we must own that they are among the best rhetorical productions of the time. In the formation of his style he appears to have endeavoured to imitate the classic writers of ancient Greece; but his language is nevertheless full of peculiarities, barbarisms, and Latinisms, probably the consequence of his long residence in Italy; and the praise which Photius (Bibl. Cod. 71) bestows upon him for the clearness of his style, must be greatly modified, for it is often harsh and heavy, and Dion seems to have written as he spoke, without any attempt at elegance or refinement.