Like earlier in this chapter, the main fighters against Babylon were the archers with their bows and arrows. They were to surround Babylon, and not let anyone get away. They were to repay her for the deeds that that she had done. They should do unto her, what she had done to them. Babylon had been arrogant in defying Yahweh, the Holy One of Israel, so that she deserved what she got.
Jeremiah recounts the destruction of the towns in Judah. When the people heard that the archers and the cavalry were coming, they abandoned their towns to go live in the brush area or in the caves among the rocks. They knew that their town would be destroyed, so no one wanted to live in them anymore.