The Kurukshetra war · Mahabharata questions
How did Bhishma die?
Bhishma fell on the tenth day of the war, shot down by Arjuna, who fought from behind Shikhandi because Bhishma would not raise a weapon against one he regarded as a woman. Able to choose his moment of death, he lay on a bed of arrows for fifty-eight nights and died after the sun turned north.
Bhishma could not be killed against his will. His father Shantanu, grateful for the vow of celibacy that let him marry Satyavati, had granted him death only at his own choosing. For ten days he commands the Kaurava army and is unstoppable, killing thousands daily, and the Pandavas cannot answer him.
On the night before the tenth day Yudhishthira goes to Bhishma camp and asks him directly how he can be defeated. Bhishma tells them: he will not fight a woman, or one who was born a woman, or one who lays down his weapons. Shikhandi, born Amba in a previous life and reborn as Drupada child, raised as a son, is the answer. On the tenth day Arjuna fights from behind Shikhandi chariot. Bhishma lowers his bow, and the arrows come.
He falls, held above the ground by the arrows in his body, and asks for a pillow; Arjuna gives him three arrows under his head, and drives another into the ground to bring up water for his thirst. He does not die there. Because the winter solstice has not passed and the sun is still in its southern course, he holds his life and waits.
He remains on that bed for fifty-eight nights, through the rest of the war and past it. Both armies come to him; after the fighting is over Yudhishthira comes with Krishna to be taught, and Bhishma answer fills the Shanti and Anushasana Parvas, the longest instruction in the epic, on kingship, law, charity and release. When the sun turns north he takes leave of them all and dies.
The epic is careful to make his death the consequence of his own vow. Everything that destroys Bhishma follows from the oath that made him great.