The archetypes are the emperors of Rome and China, who came in dynasties (or houses), with the first member tending to be appointed (variously by themselves, by their armies, or by popular assent) and then the successors appointed either by their predecessors or some electoral machinery, until a revolution threw up a new Imperial House.
In period the main empires were:
- the Byzantine Empire - which followed the Roman model;
- the Ottoman Empire in Turkey - where the main machinery for succession rested with armies and with the Muslim church;
- the Holy Roman Empire - which was started by the Popes, and came to govern, by complicated rules of election, the swathe of lands between Franconia (later to be France) in the west and the Russo-Polish lands in the east.
Essentially, in feudal terms, an Emperor could rule over kings (the Romans frequently did, in the classical period), without in any way diminishing either his authority or his claim on the lands within the subject kingdom.