1 Samuel 31:7

And when the men of Israel that were on the other side of the valley, and they that were on the other side Jordan, saw that the men of Israel fled, and that Saul and his sons were dead, they forsook the cities, and fled; and the Philistines came and dwelt in them.

The men of Israel that were on the other side of the valley - probably the valley of Jezreel, the largest and most southern of the valleys that run between little Hermon and the ridges of the Gilbea range direct into the Jordan valley. It was very natural for the people in the towns and villages there to take fright and flee; because if they had waited for 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.