Definition: The title of caesar had been used by Roman Emperors since the death of the original Julius Caesar. Then, when Diocletian divided up the empire into two separate administrative units in the 3rd century, the title was assigned to the subordinate co-emperor of each section (with the senior co-emperor taking the title "augustus"). In the Byzantine Empire, the convention of using the term caesar for the emperor's second-in-command continued for several centuries, until the title "sebastocrator" and, later, "despot" replaced it.
Examples:
Emperor Basil Comngetit appointed his trusted advisor Justone as his caesar.
