Mediceus A contains practically Books Thirty-six to Fifty-four, and Venetus A Books Forty-one to Sixty (two "decades"). As they are both the oldest copies extant and the sources of all the others, modern editors would confine themselves to them exclusively but for the fact that in each some gaps are found. In Mediceus A, for instance, two quaternions (sixteen leaves) are lacking at the start, Leaf 7 is gone from the third quaternion, Leaves 1 and 8 from the fourth; from the thirty-first (now Quaternion 29) Leaf 1 has been cut, from the thirty-third and last Leaf 5 has disappeared. Likewise in Venetus A there are some gaps, especially near the end, in Book Sixty, where three leaves are missing. Hence (without stopping to take up gaps and breaks in detail) it may be said that the general plan pursued at the present day is to adopt a reading drawn for each book from the following sources respectively:
Book 36. Mediceus A, with lacuna of chapters 3-19 incl., supplied by the mutual corrections of Vaticanus A and Parisinus B.
Books 50 to 54. Vaticanus A (vice Mediceus A).
Book 60. Venetus A, except chapter 17, sections 7 to 20, and chapter 22, section 3, to chapter 26, section 2,--two passages supplied by Mediceus B.
What knowledge has the world of the first thirty-five books of Dio's Roman History? To such a question answer must be made that of this whole section the merest glimpse can be had. It is here that we encounter the name of Zonaras, concerning whom some information will now be in order. Ioannes Zonaras was an official of the Byzantine Court who came into prominence under Alexis I. Comnenus in the early part of the twelfth century. For a time he acted as both commander of the body-guard and first private secretary to Alexis, but in the succeeding reign,--that of Calo-Ioannes,--he retired to the monastery of Mt. Athos, where he devoted himself to literary labors until his death, which is said to have occurred at the advanced age of eighty-eight. He was the author of numerous works, such as a Lexicon of Words Old and New, an Exposition of the Apostolic and Patristic Canons, an Argument Directed Against the Marriage of Two Nephews to the Same Woman, etc.; but our special interest lies in his [Greek: Chronikon] (Chronicon), a history of the world in eighteen books, from the creation to 1118 A.D.,--this last being the date of the demise of Alexis. The earlier portions of this work are drawn from Josephus; for Roman History he uses largely Cassius Dio; Plutarch, Eusebius, Appian also figure. But it has already been stated that Books Twenty-two to Thirty-five perished at an indefinitely early date; hence it follows that Zonaras has only Books One to Twenty-one at hand to use for his account of _early_ Rome; besides these he has later employed Books Forty-four to Eighty. Consequently it is possible to get many of the facts related to Dio, and in some cases his exact words, by reading Books VII to XII of this [Greek: Chronikon] or [Greek: Epitomê Historiôn] by Zonaras. It is Books VII, VIII, and IX especially which follow Books One to Twenty-one of Dio.