How is Mahabharata related to Ramayana?

Why are only Ramayana and Mahabharata classified as Itihasa?

For the learned and the uneducated in our land, Rāmāyaņa and Mahābhārata have been like their two eyes for centuries, directing them the way of the Dharma. The two poetic works do not belong to the Purāņas and are given a special place as "itihāsas".

"Itihāsam" = "iti-ha-asam" (so it happened). The "ha" in the middle means "without a doubt", "really". An "itihāsa" means a true story, including a contemporary representation. Vālmīki composed the Rāmāyana during Rāma's lifetime. Vyāsa, author of the Mahābhārata, lived during the time of the five Pandavas and witnessed the events he related in his epic.

"Pura" means "in the past". What gives an account of what happened in the past is a "Purana", although it can also contain predictions about the future. The term can also mean what was composed in the past. The "novel" genre, written in prose, emerged after a long time in poetry and drama. When the novel was first introduced in India, it was called "navīnam". When "navīnam" means new, purāna means old.

A Purāņa must have five distinctive features - (Lakshanas). The first is "Sarga" (creation of the cosmos); the second is "prati-sarga" (as expanded aeon by aeon); the third is "vamsa" (the lineage of living beings beginning with the children of Brahmā); The fourth is Manvantara (which deals with the age of the 14 Manus, ancestors of mankind during the 1000 Caturyugas) and the fifth is "vamsānucarita" (genealogy of the rulers of the nation including the sun and lunar dynasties). There are also descriptions of the earth, the heavens and the different worlds.

In the Purāņas, Vyāsa has dealt with the stories or events of the past which, of course, correspond to her name (that is, "Purāņas"). But how? Vyāsa could see into the past as well as into the future. So what he wrote about the past must be an eyewitness account. However, his contemporaries did not know about them. The Mahābhārata and the Rāmāyana are different. When these works were first introduced to the world, most people must have been familiar with the characters and events described in them. So there is no reason to doubt its authenticity. The "ha" in "itihāsa" confirms this.