Periyavachhan Pillai was a staunch devotee of Lord Tirumala Balaji. On his visit to Tirumala he was overwhelmed with Bhakthi and refused to return home
Lord Venkatesha took a form of a lad and advised Pillai to go back to his home town - Senganoor - and take care of his old parents. He gave a Saalagrama (sacred stone bearing the divine mark of God) and asked to worship.
Pillai was returning with the Saalagrama of Lord Srinivasa and kept on the banks of River Kollidam to perform ablutions and when he returned the stone disappeared
Pillai was struck with grief and started fasting to death. Lord Srinivasa appeared in his dreams and asked him to dig the same spot where he kept Salagra which now took the form of a beautiful idol form (Archaavatar).
Sri Periyavachan Pillai installed that Archavataar in Senganoor itself. The temple is about 13kms from Adhurai and 18 kms from Kumbakonam.
Senganoor is also birth place of Chandikeswara nayanar or Chandikeswarar and has a beautiful Shiva temple too