The name Thirunelli derives from the nelli, the Tamil/Malayalam word for Indian gooseberry of the Amla tree. Veda vyasa wrote the 18 existing Puranas. The Matsya Purana, Skanda Purana, Narasimha Purana, Padma Purana, and many other Puranas and Hindu texts mention the beautiful Vishnu temple as being built by Lord Brahma, located in the picturesque Sahya valley, deep in the middle of forest of unmatchable beauty, and in these texts, it is referred to as Sahyamalaka Kshetra. According to tradition, Lord Brahma was traveling round the Universe on his hamsa, when he became attracted by the beauty of the area now known as Brahmagiri Hill. Descending on that spot, Brahma noticed an idol, set in an Amla tree. Brahma recognized the idol as Lord Vishnu Himself and the place as Vaikuntha (Vishnuloka) itself. With the help of the Devas, Brahma installed the idol and called it Sahyamalak Kshetra. At Brahma's request Vishnu promised that the waters of the area would wash away all sins. (Thus, the spring and river near the temple is called Papanasini: washes away all sins).