Once, Lord Vishnu, Brahma, Priests, Devas, Gandharavas, Sages, and all other Gods went to Himalayas in order to attend the auspicious marriage of Siva & Parvathi. The Trimurthis (Brahma, Vishnu, Maheswaran) requested sage Agasthya to go and sit on shronadri, Southern bank of Pamba river to Prevent the Earth from sinking to northern side due to the weight of all invitees who came to attend the marriage. Though sage Agasthya conceded the request but he expressed his concern about loosing the chance of attending the marriage.
After the marriage Lord Shiva and Devi went to meet Agasthya muni at shronadri. There Devi became Hrithu (menstruate) and she could not go back. Devi remained there till the period of menstruation was over. The place were sage Agasthya meditated, is known as shronadri in Sanskrit and in Malayalam it is chen kunnu (Red hill). Later it is called as Chen Kunnu Urru (Urru means place) and it has been abbreviated and called as Chengannur.
The legend of Agastya’s vision of the divine marriage is associated with several temples in Tamilnadu such as Kutralam near Tirunelveli and Vedaranyam on the east coast.