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.
If this happens to be the age during which the great majority of temples in the south came into existence the explanation is here ready. It was an age when the people were anxious to bring themselves into touch with God and that could be done only by means of the cult of Bhakti which necessitated the embodying in a visible form of the all-beneficent personal God. It is possible to trace the history of many of these temples to this particular period and the work of temple-building, at least so far as Siva temples are concerned, is closely associated with the early Chola Ko-Chengan. It is demonstrable that this great Chola built temples both to Siva and to Vishnu so that he could be described by the Saivas as no less than an Adiyar (devotee) among the sixty-three. The Vaishnava Alvar Tirnmangai refers to him also as having constructed 70 temples to Siva. It is thus clear that temple-building on a large scale was only the outward exhibition of the inward ferment that led to the great development of the Bhakti school of religion.