According to the author of 1 Samuel, the Philistines and the Israelites were getting ready for a big fight, with each group standing on top of their own mountain and a big space, called a valley, between them. They were facing each other, waiting to see who would win.
1 Samuel 17:3: And the Philistines stood on a mountain on the one side, and Israel stood on a mountain on the other side: and [there was] a valley between them.
Mentions Elhanan killing Goliath, contradicting 1 Samuel 17:3 where David faces Goliath.
2 Samuel 21:19: And there was again a battle in Gob with the Philistines, where Elhanan the son of Jaareoregim, a Bethlehemite, slew [the brother of] Goliath the Gittite, the staff of whose spear [was] like a weaver's beam. [Jaareoregim: or, Jair]