The Lives of the twelve Caesars.

De vita Caesarum, known as The Twelve Caesars, is a set of twelve biographies, each about one of the Roman emperors, including one on Julius Caesar. It was written by Gaius Suetonius Tranquillus, commonly referred to as Suetonius, in 121. Considered highly significant in antiquity, The Twelve Caesars has remained a major source of Roman history.