Carving in Diana Veteranorum referring to Lucius Verus as Imperator

The title of imperator (/ˌɪmpəˈrɑːtər/ im-pə-RAH-tər) originally meant the rough equivalent of commander under the Roman Republic. Later, it became a part of the titulature of the Roman Emperors as their praenomen. The Roman emperors themselves generally based their authority on multiple titles and positions, rather than preferring any single title. Nevertheless, imperator was used relatively consistently as an element of a Roman ruler's title throughout the Principate and the Dominate. The word itself derives from the stem of the verb imperare, meaning 'to order, to command'. The English word emperor derives from imperator via Old French: Empereür.