It is written in several places in the Mahabharata that it is an "itihas" which exclusively means, "Thus occurred". The Aryan people to categorize "ancient" and "recent" events specifically coined the words "Puraana" and "Itihas". Both the words denote history that has occurred at different times. It is mentioned in the Mahabharata (Adi parva, Adhyaya 62) that the annals of the Bharata-Dynasty are recorded in the work. It has been clearly stated in the Adi parva, Bhishmaparva etc. that this is "itihas". If the intentions of the writer were to write a poem or a work of fiction, he would have stated it to be a "mahakavya" or "katha". It would be absurd to say that the Mahabharata is not an "itihas" due to its poetic nature. It was a custom in those days to write everything in poetic form. Veda Vyasa had decided to write down the "itihas" even before the initiation of the Mahabharata War. Therefore during the course of the War, Vyasa meticulously noted all the possible details. If it were a work of fiction, why would a person like Vyasa want to fill his work with such minute and unnecessary details? A number of dynasties with their long lineage of kings have been presented in this work. More than 50 kings from King Barhi to Maharaja Pandu have been recorded. Additional information about the King, his wife, his scions, his relations, etc. have been accounted in great detail. If it were just fiction, only 4-5 kings would have sufficed to build the story on. Why such mind-boggling details? The dynasties recorded in the Ramayana and the Mahabharata concur without a difference. Even the relationships between different kings and their dynasties in both the great "epics" match with each other. If both were mere "epics" written by two entirely different people at two different times, would everything match, even as regards the minor details? Many events mentioned in the Ramayana and Mahabharata are the same. Eg.: The mother of (latter) King Sagar was poisoned by his step-mother so that her child would be aborted. But the child was born nevertheless, who was therefore named Sagar. The cities established by certain kings have been noted in detail. All the characters in the "epic" are well portrayed. Every single facet of their character and important events in their life were recorded. Are such detailed accounts important in a "Maha-kavya"? The weapons mentioned in the Ramayana and the Mahabharata are somewhat the same. In fact, some weapons in the Ramayana are not mentioned in the latter "epic" Mahabharata. (eg. Soorya'stra, Yamya'stra, Shoolva'stra..etc.) [The mentioned weapons may have disappeared in the era between the two events taking place]. The Greek historian Megasthenes has stated that Chandragupta Maurya was the 138 King in the lineage of Lord Krishna. This means that Lord Krishna did exist in the bygone era and that Mahabharata did really occur. Archaeological excavations have discovered the submerged city of Dwarka. This is the same Dwarka as mentioned in the Mahabharata. [It has been reckoned that the city of Dwarka became submerged between 2000-3000 B.C.] The astronomical recordings in the Mahabharata "epic" and other scriptures (Bhagavatam), give the correct positions of the planets and stars during that time. A work of fiction would not use such astrological detail.