The History Of Herodotus Volume 1 of 2
127. So the Persians having obtained a leader willingly attempted to set
themselves free, since they had already for a long time been indignant to
be ruled by the Medes: but when Astyages heard that Cyrus was acting thus,
he sent a messenger and summoned him; and Cyrus bade the messenger report
to Astyages that he would be with him sooner than he would himself desire.
So Astyages hearing this armed all the Medes, and blinded by divine
providence he appointed Harpagos to be the leader of the army, forgetting
what he had done to him. Then when the Medes had marched out and began to
fight with the Persians, some of them continued the battle, namely those
who had not been made partakers in the design, while others went over to
the Persians; but the greater number were wilfully slack and fled.