Isaiah 22: 6-7. “And Elam bare the quiver with chariots of men and horsemen, and Kir uncovered the shield. And it shall come to pass, that the choicest valley shall be full of chariots and the horsemen shall set themselves in array at the gate.”
This is Persia, and Kir is Media, indicating that the armies of the Medes and Persians were with the armies of Assyria in the invasion of Palestine and the surrounding countries. Two hundred years later, the Medes and Persians became independent of Assyria and Babylon.
The choicest valleys being full of enemy armies indicates how huge the invading force was, and how utterly helpless Judah was without God (v. 7; 37:36-38).