Mahabharata/Jaya- Rules of the War laid out

"I agree with the rules you have laid out and promise that we will follow them as long as your side fights by the rules". Thus spoke Dhristadhyumna to Bhishma as the two commander-in-chief met along with other main warriors to discuss on the rules of the war.

Probably, this is also the time when Bhishma promised Krishna that he will ensure that Krishna takes up arms in the war. 

This was Dharm Yudh (War for Righteousness) and the rules were to be very fair as well. Rules of the war as below:

• Fighting must begin no earlier than sunrise and end exactly at sunset.

• Multiple warriors may not attack a single warrior.

• Two warriors may "duel", or engage in prolonged personal combat, only if they carry the same weapons and they are on the same mount (no mount, a horse, an elephant, or a chariot).

• No warrior may kill or injure a warrior who has surrendered.

• One who surrenders becomes a prisoner of war and will then be subject to the protections of a prisoner of war.

• No warrior may kill or injure an unarmed warrior.

• No warrior may kill or injure an unconscious warrior.

• No warrior may kill or injure a person or animal not taking part in the war.

• No warrior may kill or injure a warrior whose back is turned away.

• No warrior may attack a woman.

• No warrior may strike an animal not considered a direct threat.

• The rules specific to each weapon must be followed. For example, it is prohibited to strike below the waist in mace warfare.

• Warriors may not engage in any "unfair" warfare.

The war lasted Eighteen days. Bhishma was the Commander-in-chief for the first 10 days, then Drona for 5 days, Karna for 2 days and Shalya for a day (actually just a half) on the side of the Kauravas while Dhrishtadhyumna survived and acted in his position for the entire duration of the war.