Cassius Dio and Ulpian: Article by Robert L. Cleve in Ancient History Bulletin on the contrasting accounts of the regency during the reign of Severus Alexander.
Dio Cassius: Brief biography of Cassius Dio Coccetanus from the 1911 Encyclopedia Britannica.
Dio Cassius (c. A.D. 40 - 110) - Cassius Dio Cocceianus: PDF and hypertext selections from the 1914 Cary/Loeb translation of the Roman History.
Lacus Curtius: Cassius Dio's Roman History: Full text by chapter of the 1914 English translation by Earnest Cary.