Battle of Mahabharata is a historical fact. There are differences in opinion about the duration of the battle. Want to know the duration thereof.
As per Mahabharata: Adi Parva, the great war of Mahabharata happened for 18 days :
Bhishma acquainted with choice of weapons, fought for ten days. Drona protected the Kaurava Vahinis for five days. Karna the desolator of hostile armies fought for two days; and Salya for half a day. After that lasted for half a day the encounter with clubs between Duryodhana and Bhima. At the close of that day, Aswatthaman and Kripa destroyed the army of Yudishthira in the night while sleeping without suspicion of danger. ~Mahabharata: Adi Parva
As you can see above, Aswatthama and Kripa destroyed Pandavas army in night after the close of 18th day.
Jaya, the core of Mahabharata, is structured in the form of a dialogue between Kuru king Dhritarashtra (born blind) and Sanjaya, his advisor and chariot driver. Sanjaya narrates each incident of the Kurukshetra War, fought in 18 days, as and when it happened.