This section is from the book "Some Contributions Of South India To Indian Culture", by S. Krishnaswami Aiyangar. Also available from Amazon: Some Contributions of South India to Indian Culture.
This idea of Bhakti or devotion to a personal god is traceable in the earliest extant pieces of Tamil literature. Some of the oldest poems contain references to theistic gods both Vaish-nava and Saiva, and what is more to the four vyuhas for which Sir R. G. Bhandarkar could find no clear reference in Sanskrit literature before the 1st century B. C. The Paripadal an ancient poem of the Sangam collection contains among one of its oldest pieces an unmistakable reference to the four vyuhas of Vishnu. Its poem 3 is devoted entirely to Vishnu, for whom there are a number of other poems in the same collection where various other Vedic aspects of the God are adverted to, but nothing so clear as this to the four vyuhas. The worship of Krishna and Baladeva seems to have been quite an ordinary feature of Tamil civilization in the earliest periods of which we have knowledge. One of the oldest of South Indian1 shrines for which we have a reference is devoted to the worship of Krishna. This feature of that temple seems to have continued till about the 8th century A. D. Among the numbers of temples mentioned as having existed in Kaveripattanam, the capital of the Cholas in the first century of the Christian era figure temples to Krishna and Baladeva. Temples to these two are found mentioned among the four principal shrines of Madura, namely those to Siva, Krishna, Baladeva and Subramanya. These are again the four deities celebrated by the poet Narkirar the President of the Third Sangam in Madura. A number of minor deities do of course come in for reference particularly among the deities to whom temples were found in Kaveripattanam. This multitude of gods and godlings to whom temples were in existence in the same city is referred to in the Buddhistic work Manimekhalai in general terms; all temples beginning from that to Him with an eye in the forehead and ending with that to the Bhuta in the public square. A similar sentiment in Maduraik-Kanji was already referred to. The early grammatical work Tolk-appiyam referring to the presiding deities over the various divisions of a country refers to the forest country presided over by Krishna, the hill country presided over by Subrahmanya, the plain country presided over by Indra (the king), the country on the sea-shore presided over by Varuna; the Vedic gods Varuna and Indra being brought into line with Subrahmanya and Krishna. We see therefore the germs that fructified into the school of Bhakti, both Vishnu-Bhakti and Siva-Bhakti, in the Tamil country already, and they exhibit the features which the northern school of Bhakti does in all its detail. In the course of development South India came to be regarded as the special provenance of Bhakti although the Vedic form of ritualistic religion was maintained by the colonies of Brahmanas who had come and settled down, and who were countenanced and maintained by the ruling powers and society as a whole. The unmistakable beginning of this development we could see already in early Tamil liteature. Several of the features peculiar to the Gita itself are found in the poems devoted to Vishnu, and even some of those more abstruse features for the worship of God, reaching behind the Bhagavat Gita itself to the Upa-nishads.
1 Tirumalirunjolai near Madura.