But he owed his success to prudent management, and not to courage or military skill.
On the north-eastern frontier, occupying the low country now known as Talish and Ghilan, was a powerful tribe called Cadusians, probably of Arian origin, which had hitherto maintained its independence.

This would not be surprising, if we could accept the statement of Diodorus that they were able to bring into the field 200,000 men.

But this account, which probably came from Ctesias, and is wholly without corroboration from other writers, has the air of a gross exaggeration; and we may conclude from the general tenor of ancient history that the Cadusians were more indebted to the strength of their country, than to either their numbers or their prowess, for the freedom and independence which they were still enjoying.

It seems that they were at this time under the government of a certain king, or chief, named Aphernes, or Onaphernes.
This ruler was, it appears, doubtful of his position, and, thinking it could not be long maintained, made overtures of surrender to Astyages, which were gladly entertained by that monarch.

A secret treaty was concluded to the satisfaction of both parties; and the Cadusians, it would seem, passed under the Medes by this arrangement, without any hostile struggle, though armed resistance on the part of the people, who were ignorant of the intentions of their chieftain, was for some time apprehended.
The domestic relations of Astyages seem to have been unhappy.