positively known. He has been credited with the use of Livy, of
Coelius, of Appian, and of Dionysios of Halicarnassos, but the
traces are not definite enough to warrant any dogmatic assertion.
Perhaps he knew Tacitus and perhaps Suetonius: the portrait of
Tiberius is especially good and was probably obtained from an author
of merit. But there were in existence a great multitude of books
inferior or now forgotten besides the works of the authors above
mentioned; and Dio's History in general shows no greater evidence of
having been drawn from writers whom we know than from others whom we
do not know.

We have already noticed Dio's similarity to Thukydides in style,
arrangement, and emotional attitude. There remains one more bond of
brotherhood,--the speeches. Just as the sombre story of the
Peloponnesian conflict has for a prominent feature the pleas and
counterpleas of contending parties, together with a few independent
orations, so this Roman History is filled with public utterances of
famous men, either singly or in pairs. Dio evinces considerable
fondness for these wordy combats ([Greek: hamillai logôn]). About one
speech to the book is the average in the earlier portion of the work.
The author probably adapted them from rhetorical [Greek: meletai], or
essays, then in existence. He was himself a finished product of the
rhetorical schools and was inclined to give their output the greatest
publicity. The most interesting of these efforts,--some go so far as
to say the only one of real interest,--is the speech of Mæcenas in
favor of the establishment of monarchy by Augustus: this argument
undoubtedly sets forth Dio's own views on government. Like the rival
deliverance of Agrippa it shows traces of having undergone a revision
of the first draught, and it is more than probable that the two did
not assume their present shape until the time of Alexander Severus.