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.
It is this state of things, of which we gain a direct glimpse only from Tamil literature, that gives character to South Indian History - for the earliest period of the history of the Tamil country. Brahmanism having found a welcome home in this region when Buddhism was in the ascendency in North India, pursued its path unmolested, if it did not actually occupy a position of advantage in comparison with the other two religions. This freedom made the Tamil country at this period, as it proved in other later periods, a special refuge to Aryan culture whenever it was hard pressed in the North. From this period onward Brahmanism both in its early and in its later developments went on continuously unmolested, not uninfluenced, by the various changes that took place across the Tamil frontier. In this body of literature and in this particular period we see a certain amount of development in the agamic worship of the Vaish-nava Pancharatrins. There is nothing exactly to show that the Saiva agama did not come in along with this into the Tamil country although we have not come across any direct statement of it so far in the same manner as the Vaishnava. That with the spread of Buddhism and Jainism there was a collateral development of the Orthodox Brahmanism in the middle country of northern India seems warranted by the position of these religions in the Tamil country. The rise of the school of Bhakti which Sir It. G. Bhandarkar laboured hard, but successfully, to prove as a normal development from the Upani-shadic culture, receives welcome support from the position of this particular school of Brahmanism in the south. This establishes an intimate connection, in the age to which this body of literature has special reference, between the north and the south. This special development could not have been on this side of the Christian era if the intimate connection of the development both in the north and in the south has to be taken as established, as we have to, on the basis of this evidence.