Schaff's Bible Dictionary
MONEY-CHANGERS. Every Israelite who had reached the age of twenty was required by the Law, Ex 30:13-15, to pay one half-shekel, as an offering to Jehovah, into the sacred treasury whenever the nation was numbered. As this offering should be paid in exact Hebrew coins, dealers in such coins established their booths in the temple and exacted high premiums from the Jews, who from all parts of the world came to Jerusalem during the great festival.
But they were expelled by our Lord. Matt 21:12; Mark 11:15.