This is the place where Absalom, while he was alive, set up a monument, realizing that he would not be able to inherit the throne.
2 Samuel 18:18Now Absalom in his lifetime had taken and set up for himself a pillar in the King’s Valley, for he said, “I have no son to keep my name in remembrance.” He called the pillar after his own name, and it is called Absalom’s Monument to this day.