Period in history and the style of art that developed when the Roman Republic ceased to exist and Rome expanded its territory and was ruled by emperors. The period is generally considered to begin with Octavian's victory at the Battle of Actium in 31 BCE, and to last through the rule of the Severans. For later emperors, see "Late Antique." Note that some classifications include the Tetrarchic, Constantinian, and the Holy Roman Empire in the "Roman Empire.".