Samasaptaka Parva is the sixty sixth Upa parva included in the seventh Maha parva named as Drona parva. Vaishampayana continued narration to Janamejaya in reply to his queries as follows.
How Drona had arranged the Mahabharata war on the twelfth day of war?
Under the commander-in-chief Drona, the Mahabharata war was fought for three days from the eleventh day morning up to the thirteenth day late night. There was rest for the fighting soldiers on the eleventh day night and on the twelfth day night but the war was not stopped.
Initially, Drona had thought the war should be fought by the soldiers in four parts taking shifts like a relay. One third of the soldiers should go for relief or for personal reasons out of the battle field into their war camps but one third should be always fighting with the enemy soldiers.

Karna was helping Drona on war time basis. Drona had arranged all medical facilities for the needy soldiers by order of Duryodhana. Drona had also arranged all kinds of food facilities for the needy soldiers. Pork (pig-meat) was supplied to the interested non-vegetarian soldiers with the choice of alcohol also. Drona had arranged all resting facilities for the needy soldiers in his war camps.
Ashwathama was not allowed by Duryodhana to fight directly in the battle field. He was allotted the risk of army intelligence, timely reporting of the war plans of the opposite side soldiers. So he was reporting to his father or to Duryodhana timely, avoiding his field exposure. Some of the soldiers started from their camp on the eleventh day morning but continued to proceed on fighting on the twelfth day also. The Samasaptaka warriors had not returned to their camps but went on fighting and died on the twelfth day.