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 period must also have been one of great religious activity. Many of the existing temples came into existence during this period and most of them in Kanchi and the surrounding locality received encouragement and extension. The town of Kanchi itself is so full of these Pallava monuments that it would be possible for one to make a complete study of Pallava art and architecture without going out of it. The great renaissance of religion and literature characteristic of the age of the Guptas in the north found a reflex during the age of the Pallavas in Kanchi,
Both Saivism and Vaishnavism, the two offshoots of the school of Bhakti, took form and shape during this period. Literature bearing upon both of these in Tamil is almost entirely the product of the age of the Pallavas. Of the 63 Saiva devotees one of the earliest is the Chola king Ko-Sengan who must have followed the age of the Sangam very closely. We have shown elsewhere1 that the earliest of the Vaishnava Alvars were in all probability contemporaries of the Tondaman-Ilam-Tiraiyan himself. It is not at all unlikely that some of the sixty-three Saiva Adiyars may be referable to an age as early as these. The latest among the Alvars is Tiruman-gai Alvar, who lived as certainly as it is possible for us to know the fact, in the middle of the eighth century. The latest of the Saiva Adiyars, Sundaramurti, lived perhaps a generation later in the closing period of the Pallava dominance in the south. The greatest among the Adiyars Sambandar and Appar, two of the three most celebrated among the Adiyars, were undoubtedly contemporaries of Narasimha I. Thus we see the schools of Bhakti, the early features of which we already find reference to in the Sangam literature, began their great development under the Pallavas and took the form that they have at present, in this period.
1 Early History of Vaishnavism: Oxford University Press.