1 Samuel 17:1-3

Now the Philistines gathered their armies for battle; and they were gathered at Socoh which belongs to Judah, and they camped between Socoh and Azekah, in Ephes-dammim.

Saul and the men of Israel were assembled and camped in the Valley of Elah, and they drew up in battle formation to confront the Philistines.

The Philistines were standing on the mountain on one side, while Israel was standing on the mountain on the other side, with the valley between them.