Lucius Cassius Dio
17th century illustration of Dio
Native name	Δίων Κάσσιος
Born	c. 165 AD Nicaea, Bithynia
Died	c. 235 AD (aged approx. 70) Bithynia
Occupation	Historian, senator, praetor, proconsul, consul
Nationality	Roman
Subject	History
Notable works	History of Rome
Relatives	Cassius Apronianus (father), Cassius Dio (grandchild or great-grandchild)

Lucius Cassius Dio (c. 165 – c. 235),^[i] also known as Dio Cassius (Ancient Greek: Δίων Κάσσιος Dion Kassios), was a Roman historian and senator of maternal Greek origin. He published 80 volumes of the history of ancient Rome, beginning with the arrival of Aeneas in Italy. The volumes documented the subsequent founding of Rome (753 BC), the formation of the Republic (509 BC), and the creation of the Empire (27 BC) up until 229 AD, during the reign of Severus Alexander. Written in Koine Greek over 22 years, Dio's work covers approximately 1,000 years of history.

Many of his books have survived intact, alongside summaries edited by later authors such as Xiphilinus, a Byzantine monk of the 11th century, and Zonaras, a Byzantine chronicler of the 12th century.

Cite error: There are <ref group=lower-roman> tags or {{efn-lr}} templates on this page, but the references will not show without a {{reflist|group=lower-roman}} template or {{notelist-lr}} template (see the help page).