material for the period down to Severus' death,[1] that he had read everything of importance on the subject,[2] and that twelve years was the time occupied in composing the work.[3] The period of these labours may be roughly estimated as the years 200-222. The lexicographer Suidas attributes five other works to Dio; but it is practically certain that only one, or possibly two, of these shorter works can have been written by him. The Life of Arrian, who was a fellow-Bithynian as well as a fellow-historian, may actually have been the work of Dio. If he ever wrote an account of Hadrian's reign, it was doubtless incorporated in his large work, as was the case with his first two treatises; but it is strange that he should have made no mention of it.
The whole period of nearly a thousand years covered by his history falls into three main divisions according to his own statements.[4] The first is the period of the republic, when political action rested with the senate and the people; the facts were public property, and even if distorted from personal motives by some writers, could readily be ascertained from others or from the public records. The second period extends from the establishment of the monarchy to the death of Marcus Aurelius. Under the emperors action was no longer taken openly, and such versions as were given to the public were naturally received with suspicion. Dio must now
