Siva Lingam at Thayumana Swamy shrine is represented by an imposing natural projection of rock over 5 feet high.
As per the Legends, an ardent devotee Ratnavati became pregnant, her mother went to help her during delivery time. Ratnavati lived on the north bank of the river Cauvery, which flows thru Tiruchirapalli. As the baby delivery time approached, Ratnavati's mother had to go to Tiruchirapalli, crossing the river which was flooding.
A worried Ratnavati prayed to the Lord and found her mother by her side. The baby was born safely. Soon after the floods receded, her mother reached the place. When she asked how she managed to deliver the baby, then they came to know that it is Lord who came in the form of her Mother. Thayum ana means "One who became the Mother".
It is believed that the original temple entrance was facing East and now it is in opposite direction. As per the Legends, Sage Sarama an ardent devotee of Lord Siva used to grow a special flower in his garden for the Lord. One day he found a guard of King Parantaka Chola ( 907 A.D - 955 A.D) was taking away the flowers. The sage complained to the King about the theft. King ignored the complaint after knowing from the guard that queen ordered for these flowers. Sage cried a lot before the Lord as he was not able to perform Pooja. Lord Siva became angry that He averted his benign glance from the capital city of Urayiur. This caused a rain of soil to fall on the city, worried king prayed for Vekkali Amman ( a form of Goddess Parvati), who pacified the Lord.