Jamieson, Fausset and Brown on 1 Samuel 31:7

7. the men of Israel that were on the other side of the valley--probably the valley of Jezreel--the largest and southernmost of the valleys that run between Little Hermon and the ridges of the Gilboa range direct into the Jordan valley. It was very natural for the people in the towns and villages there to take fright and flee, for had they waited the arrival of the victors, they must, according to the war usages of the time, have been deprived either of their liberty or their lives.

1Sa 31:8-10. The Philistines Triumph over Their Dead Bodies.