An empire is a political unit made up of several territories, military outposts, and peoples, "usually created by conquest, and divided between a dominant center and subordinate peripheries". The center of the empire exercises political control over the peripheries. Within an empire, different populations have different sets of rights and are governed differently. Narrowly defined, an empire is a sovereign state whose head of state is an emperor or empress; but not all states with aggregate territory under the rule of supreme authorities are called empires or are ruled by an emperor; nor have all self-described empires been accepted as such by contemporaries and historians.
The Ancient Greek kingdom of Macedonia
Maurya Empire of India at its greatest extent under Ashoka the Great
The three Muslim Gunpowder empires: Mughals, Safavids, and Ottomans in 18th century
Al Udeid Air Base in Qatar
The word emperor can mean the male ruler of an empire. Empress, the female equivalent, may indicate an emperor's wife, mother/grandmother, or a woman who rules in her own right and name. Emperors are generally recognized to be of the highest monarchic honour and rank, surpassing kings. In Europe, the title of Emperor has been used since the Middle Ages, considered in those times equal or almost equal in dignity to that of Pope due to the latter's position as visible head of the Church and spiritual leader of the Catholic part of Western Europe. The emperor of Japan is the only currently reigning monarch whose title is translated into English as "Emperor".
Gaius Octavianus Caesar "Augustus", or simply Augustus, was the first emperor of the Roman Empire, reigning from 27 BC until his death in AD 14.
A statue of dictator Julius Caesar.
Under Justinian I, reigning in the 6th century, parts of Italy were for a few decades (re)conquered from the Ostrogoths: thus, this famous mosaic, featuring the Byzantine emperor in the center, can be admired at Ravenna.
Holy Roman Emperor Charles V in the 1550s, after Titian