"Pax Romana" is an idea first presented by Edward Gibbon in the first chapter of The History of the Decline and Fall of the Roman Empire. He refers to a period of "moderation" initiated by Augustus and imitated by his successors. Conquest became less beneficial and the Emperors became content with the borders of the Empire. Generals like Germanicus, Suetonius Paulinus, Agricola, and Corbulo were checked and recalled by the Emperors during their victories. Gibbon lists three exceptions to the "moderation" policy between Augustus and Marcus Aurelius - the conquest of Britannia under Claudius, the conquest of Dacia under Trajan and Trajan's "dangerous" invasion of the east.