The noise of a multitude in the mountains. I do not know why Isaiah should not have been "thinking of his geography" (Cheyne). As soon as the Greeks knew anything of the Persians, they knew of them as a mountain people, and attributed their valor and their handy habits to the physical character of their country (Herod; 9.
ad fin.). Jeremiah connects the invading army which destroyed Babylon with mountains, when he derives it from. Ararat (comp. Genesis 8:4), Minni (Armenia), and Ashchenaz (Jeremiah 51:27). At any rate, the mention of "mountains" here is very appropriate, both Media and Persia being, in the main, mountainous countries.
A great people; or, much people—not necessarily of one nation only. The host of the battle; rather, a host of war; i.e. a multitude of men, armed and prepared for war.