Wikipedia
Kavirajamarga
Kavirajamarga (850 C.E.) is the earliest available work on rhetoric, poetics and grammar in the Kannada language. It was written by the famous Rashtrakuta King "Nrupatunga" Amoghavarsha I, and some historians claim it is based partly on an earlier Sanskrit writing called Kavyadarsa. Some historians believe Kavirajamarga may have been co-authored by a poet in the king's court, the Kannada language theorist Sri Vijaya.
The name literally means "Royal Path for Poets" and was written as a guide book for poets and scholars (Kavishiksha). From references made in this writing to earlier Kannada poetry and literature it is clear that a considerable body of work in prose and poetry must have existed in the preceding centuries.