The name Thirunelli derives from the word nelli, the Malayalam/Tamil equivalent for Indian gooseberry (Amla) tree. Once when Lord Brahma while traversing the world, saw an idol of Lord Vishnu resting on an amla tree in the valley and thus the place came to be named Thirunelli. In Padma Purana (written by Veda Vyasa) there is mention of a beautiful Vishnu temple located in the picturesque Sahya valley deep in the middle of the forest. Thirunelli temple is also referred to as Amalaka temple and Sidha temple.
History depicts Chera king Kulasekharan as the founder of this temple. He lived between A.D 767 and A.D 834. After a brief reign, he relinquished the throne and started missionary work to propagate Vaishnava order. It was he who wrote the Sanskrit work Mukundamaala in which he earnestly prays to Lord Vishnu to instill in him devotion.
On stylistic ground this looks as a typical Kerala temple. The inner sanctorum is surrounded by a tile roofed structure. And there’s an open courtyard around the sanctorum. At the east, in front of the entrance is a granite lamp-post. Curiously enough the flag post is absent, though one can spot a hole on the floor where it ought to be.
Along the outer wall of the temple is a cloister made of granite pillars cut in cubical style. This part of the temple architecture is slightly unusual for a Kerala temple. And it seems the cloister work was never completed. The story goes that once the King of Coorg, tried to renovate this temple. When he was half way through, the Vellattiri King who owned the temple objected to the same. Thus renovation was discontinued. Even today we can see proof of the half finished renovation work.
It is an undisputed fact that Thirunelli was once an important town and pilgrim centre in the middle of inaccessible jungled valley surrounded on four sides by mountains. The copper plates of the 10th century and a few books of the later centuries convincingly prove that Thirunelli was an urban hub in South India at least from 10th century onwards. Also in the dense forest surrounding the temple, the ruins of two ancient villages can be found. Recent excavations at the time of paving roads have yielded coins of 9th and 10th centuries. There are two copper plate inscriptions pertaining to the history of Thirunelli Temple. They date back to the period of Bhaskara Ravivarma, a ruler of the Chera kingdom who lived in the 10th century. First inscription is written in 999 A.D (37th year of the rule of Bhaskara Ravivarma) and the second inscription in 1008 A.D (46th year of the rule of Bhaskara Ravivarma). The first one is regarding the allotment of the royal land in Thirunelli to the temple, to meet its expenses towards daily poojas. The second inscription deals with the procedures to be observed during the temple visit of the ruler of the Puraikeezhar Kingdom. The donor in the first inscription is Kunhikutta Varman VeeraKurumpurai who ruled Kurumbranaad. The donor in the second inscription is Sankaran Godavarman of Purakeezhar dynasty. Both the inscriptions shed light to the ruling customary practices and social relations of the time.
“Unniyachi Charitham” is a poetical work written by Thevan Chirikumaran (Devan Sreekumaran) between 12th and 13th centuries. In this poem there is an elaborate description of Thirunelli, Papanasini and the four borders of Thirunelli. Among them 17 lines are in prose. There are two poetic stanzas each having 4 and 6 lines. It is indeed a travelogue in which the poet imagines himself as a Gandharvan interested in travel and tour. Observing the customs, it is after visiting Thrissilery temple that the Gandharva comes to Thirunelli.
"Kokila Sandesham" is a book written by Udhanda Sashthrikal of Kanchipuram during the 15th century. The hero of this poem lived in his house at Chendamangallur near Kochi. He happens to be airlifted from the house by some airy spirits and gets stranded at Kancheerpuramm in Tamilnadu. Then the hero entrusts a cuckoo to intimate his wife about his peril. This cuckoo on the way reaches Thirunelli to worship the Perumal in the temple. The 40th stanza of this poem describes the visit of the Cuckoo in Thirunelli Temple. The author Udhanad Sashthrikal lived from 1405 to 1475. It is certain from the descriptions about Thirunelli that the poet had personally visited the temple there.
During early times, water for temple use was brought from Papanasini stream. During a draught period, the wife of Chirackal Raja who was a member of the famous Vaarikkara Nayanar tharavad, came with her attendants to temple to worship. She asked the Priest some water to dissolve the sandal, which he was not able to give. Being enlightened about the water scarcity in the temple she asked her attendants to solve the problem. They found out the water source called Varaham in the thick forest. From there the water was brought, using bamboo halves for immediate use. Subsequent to her return home, she sent men and materials to construct the present stone aqueduct to bring
uninterrupted water supply to the temple. The granite open channels are supported by pillars with interesting murals carved on. Even till date, cold mountain stream water gush out of this aqueduct.