The invader is introduced with the same mysterious indefiniteness as in Jeremiah 4:13. From Dan; i.e. from the northern frontier (see on Jeremiah 4:15). Trembled; rather, quaked (so Jeremiah 49:21). His strong ones.
The phrase "strong ones" generally denotes oxen, but here (as in Jeremiah 47:3; Jeremiah 50:11) horses.