The ephorus were leaders of ancient Sparta and shared power with the two Spartan kings. The ephorus were a council of five elected annually who swore "on behalf of the city", while the kings swore for themselves.
Herodotus claimed that the institution was created by Lycurgus, while Plutarch considers it a later institution. It may have arisen from the need for governors while the kings were leading armies in battle. The ephorus were elected by the popular assembly, and all citizens were eligible for election. They were forbidden to be reelected. They provided a balance for the two kings, who rarely cooperated with each other. Plato called them tyrants who ran Sparta as despots, while the kings were little more than generals. Up to two ephorus would accompany a king on extended military campaigns as a sign of control, and they held the authority to declare war during some periods in Spartan history.
According to Plutarch, every autumn, at the crypteia, the ephorus would pro forma declare war on the helot population so that any Spartan citizen could kill a helot without fear of blood guilt. This was done to keep the large helot population in check.
The ephorus did not have to kneel down before the Kings of Sparta and were held in high esteem by the citizens, because of the importance of their powers and because of the holy role they earned throughout their functions. Since decisions were made by majority vote, this could mean that Sparta's policy could change quickly, when the vote of one ephor changed (e.g. in 403 BC when Pausanias convinced three of the ephorus to send an army to Attica). This was a complete turn around to the politics of Lysander.
Cleomenes III abolished the ephorus in 227 BC, but they were restored by the Macedonian king Antigonus III Doson after the Battle of Sellasia in 222 BC. While Sparta fell under Roman rule in 146 BC, the position existed into the 2nd century AD, when it was probably abolished by the Roman emperor Hadrian and superseded by Imperial governance as part of the province of Achaea.
The ephorus held numerous duties including legislative, judicial, financial, and executive duties.  They had the power to indict a king, who would then be tried before the ephorus and gerousia. The gerousia were the Supreme Court of Sparta. Historians Paul Cartledge, Bury and Huxley agree that the ephorus attained powers as great as the kings during the 7th century BC.
The word "ephorus" (Greek ἔφοροι éphoroi, plural form of ἔφορος éphoros) comes from the Greek ἐπί epi, "on" or "over", and ὁράω horaō, "to see", i.e. "one who oversees" or "overseer".
 Xenophon, Constitution of Sparta they collected taxes and in forced laws in Sparta. 15.7
 Life of Lycurgus, 28, 3–7
 Xenophon, Constitution of Sparta 15.6; Xenophon, Hellenica 2.3.9–10; Plutarch, Agis 12.1, 16.2; Plato, Laws 3.692; Aristotle, The Politics 2.6.14–16; A.H.M. Jones, Sparta (Oxford: Basil Blackwell, 1967), p. 26; Robert Struble, Jr., Treatise on Twelve Lights, chapter six, subsection entitled "Ancient Greece"
 Donald Kagan, The Outbreak of the Peloponnesian War. page 29. Ithaca/New York 1969, ISBN 0-8014-9556-3.
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