He is called Adikavi since the moment he cursed an hunter on killing Kraunch bird in a totally original chhandas.Narada advised Valmiki to write in the same poetic meter the life and deeds of Rama.He, concising about ten grammar schools prevalent during his time, wrote the master book of grammar named Ashtadhyayi which served as beacon for the later period.
The Pratishakhyas explained the forms of the words and other grammatical points. During this period a vast literature -Vedas, Brahmana-Granthas, Aranyakas, Upanishads and Vedangas had come to existence which could be termed as Vedic Literature being written in Vedic Sanskrit. C.) was a great landmark in the development of Sanskrit language.
He wrote the Ramayana the great-epic which had the great impact on the later literature.
Even today the latest poetry is written on the line of Valmiki. The second epic Mahabharata was written by Krishanadwaipayana Vyasa which is known as encyclopedia of knowledge.
Aranyakas and Upanishads discuss the internal meaning of the Vedas and the path of renunciation – Moksha Purushartha.
Pratishakhyas explain the grammatical issues of the Vedas. Shiksha, Vyakarana, Kalpa, Chhandas, Nirukta, and Jyotish help to understand the Vedas.