Gaius Suetonius Tranquillus, commonly referred to as Suetonius, was a Roman historian who wrote during the early Imperial era of the Roman Empire. His most important surviving work is De vita Caesarum, commonly known in English as The Twelve Caesars, a set of biographies of 12 successive Roman rulers from Julius Caesar to Domitian. Other works by Suetonius concerned the daily life of Rome, politics, oratory, and the lives of famous writers, including poets, historians, and grammarians. A few of these books have partially survived, but many have been lost.