The earliest form of Tamil literature found in inscriptions and texts is referred to as Old Tamil. It is the oldest attested stage of the Tamil language, and is dated from the 3rd century BCE to the 7th century CE. Old Tamil is characterized by a number of features that distinguish it from later stages of the language, including a different phonological system, a different grammatical system, and a different lexicon.
Classical Tamil is the next stage of the Tamil language, and is dated from the 8th century CE to the 16th century CE. Classical Tamil is characterized by a number of features that distinguish it from Old Tamil, including a more complex phonological system, a more complex grammatical system, and a more complex lexicon.
Middle Tamil is the next stage of the Tamil language, and is dated from the 17th century CE to the 19th century CE. Middle Tamil is characterized by a number of features that distinguish it from Classical Tamil, including a simplification of the phonological system, a simplification of the grammatical system, and a simplification of the lexicon.
Modern Tamil is the latest stage of the Tamil language, and is dated from the 20th century CE to the present day. Modern Tamil is characterized by a number of features that distinguish it from Middle Tamil, including a further simplification of the phonological system, a further simplification of the grammatical system, and a further simplification of the lexicon.
In conclusion, the earliest form of Tamil literature found in inscriptions and texts is referred to as Old Tamil.