Charles Ellicott Commentary 1 Samuel 31:9

"And they cut off his head, and stripped off his armor, and sent into the land of the Philistines round about, to carry the tidings unto the house of their idols, and to the people." — 1 Samuel 31:9 (ASV)

And they cut off his head, and stripped off his armour. —Only Saul’s head and armour are mentioned here, but on comparing 1 Samuel 31:12, where the bodies of his sons are especially mentioned, it is clear that this act was not confined to the person of the king. The sense of the passage there is, the heads of the king and his three sons were cut off, and their armour stripped from their bodies. The heads and armour were sent as trophies around the different towns and villages of Philistia, and the headless corpses were fastened to the wall of the city of Beth-shan.