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What is a…
tetrarch

Strictly speaking, this is the title of a ruler over a 4th of a Roman province, but the word also denotes a ruler of a province generally (Matthew 14:1; Luke 3:1, 19; 9:7; Acts 13:1)

Herod and Phasael, the sons of Antipater, were the first tetrarchs in the Land of Israel.

Herod the tetrarch had the title of king (Matthew 14:9).