Josephus describes the effect that John the Baptist had on the Jews in Book 18 of Antiquities of the Jews:
"Now many people came in crowds to him, for they were greatly moved by his words. Herod, who feared that the great influence John had over the masses might put them into his power and enable him to raise a rebellion (for they seemed ready to do anything he should advise), thought it best to put him to death. In this way, he might prevent any mischief John might cause, and not bring himself into difficulties by sparing a man who might make him repent of it when it would be too late. Accordingly John was sent as a prisoner, out of Herod's suspicious temper, to Macherus, the castle I already mentioned, and was put to death."