On the 10th day of the Mahabharata War, the Pandavas came to sad conclusion that unless they killed their grandfather Bheeshma, there would be no end to the battle. Knowing that Bheeshma had vowed to never take up arms against a woman, they had Shikandi lead their battle formation. Shikandi was viewed as either the reincarnation of Amba, whom Bheeshma had grievously wronged, or as a man who had been born as a woman, with both of these scenarios giving him an advantage against Bheeshma.
Yudhishtra formed the sacred Deva Vyuha, the formation of the gods. Behind Shikhandi were Arjuna and Bheema. Supporting them were Abhimanyu and Gatotkacha. Satyaki, Dhristadyumna, Virata and Drupada flanked them. Yudhishtra, Nakula and Sahadeva lined up behind them, at the heart of the formation.
The Kauravas assembled their legions in the Asura Vyuha, the demon formation. Bheeshma stood at the forefront of the army with Drona at his side, and Duryodhana, Ashwathama, Bhagadatta, Kritavarma and Kripacharya following him.
This would be the day that saw the end of Bheeshma, as well as the beginning of the end of the great war.
Philosophy of the Formations
Nothing much to say here. They formed the Angel and Demon battle formations. Good vs Evil. Righteous vs Unrighteous. Can't get more obvious symbolism than that.
Map of the Battlefield