Pavala Vannar and Pachai Vannar Perumal temples, Kanchipuram - a Divyadesam shrine

Pavala Vanna nather temple, Kanchipuram. divinebrahmanda.com
Sri Pachai Vanna Perumal Temple in Kanchipuram pinterest.co.uk
Kanchipuram town has 18 Divyadesam temples (dedicated to Vishnu)  and among them the two temples of Pacchai and Pavala Vannan perumal together form a ''Divyadesam''. 

Located  on the same street close to  Sri Kamakshi Amman temple in Kanchipuram  are  the Pacchai and Pavala Vannan perumal  temples  that are considered as one place of worship. Both temples  together form the  ''Divvyadesam'' shrine glorified by the Tamil Azhawar saints despite the fact no Mangalasasanam is done in the   Pacchai Vannar sannadhi so far for unknown reasons. 

It is to be noted that Pacchai Vannar, also referred to as "Maragatha Vannar" is a form  of Lord Shiva, whereas Pavala Vannar a form  of Parasakthi (sister of Sri Vishnu). So, devotees must visit both shrines and should not leave the other.  Sri Pachai Vannar, who is in emerald green, is in a sitting posture on the serpent Adishesha  (Irundha Thirukkolam on Aadhiseshan). Very few Perumal temples across India, in particular, Tamil Nadu  have this kind of sitting posture on the giant serpent and, obviously, it is one of a kind.  The belief is when devotees worship at these perumal temples, they, in a way, also worship Lord Shiva and Parvathi. 

Here, lord gave darshan to Brighu Maharishi (sage) who raised many questions about the pupose of his avatar (incarnation) as Rama in Thretha Yuga, abduction of Sita by Ravanna, assistance  from  Sri Anjenaya and others, Lord explained to him that his avatar was to make the people understand how it is important to lead a dharmic life, following the right path, respecting elders and people around them and how the good emerges victorious at the end over the evil, etc. Lord Shiva took the form of  Sri 'Anjenaya' and Sri  Lakshmana took the form of lord's serpent bed 'Adishesha'. When the sage wanted to have the darshan of Adishesa, obliging his request, he appeared as ''Jyothi'' (bright light) on his head, This is the reason why Naga (serpent) Deepam is lit in the shrine of the goddess. 
Pachnai Vanna nather temple, Kanchipuram divinebrahmanda.com
According to the legend associated with these temples, once, at the request of God Brahma, Vishnu appeared as a holy fire  from the Yagna performed by Brahma when his consort Saraswati, in a fit of rage and, in association with demons (Asuras), wanted to stop the ritual. Vishnu  pacified Brahma's consort and the yagna was successfully completed later. The sanctum has no images of goddesses as the lord  gave darshan to the sage. Devotees offer him tulsi mala and green-colored cloth as the color of planet Mercury is green. Besides, archana is done by the devotees to avoid the negative  effects of Budha on them.

Pavala Vanna Nather temple is just close-by on the opposite side and here, lord's consort is Mahalashmi (Pavalavalli Thayyar) who has a separate shrine. This temple is a small one unlike Pacchai Vanna Perumal temple which is slightly biger and has many stone sculptures. The shrine carries the chakra, a symbol of Sri Vishnu.  Here the Perumal is in coral red color and is  also known as "Paramapatha Nathan"; his   thirumugham is facing  West. The Mangalasasanam was  done by saint Thirumangai Azhwar. The red coral color of perumal is symbolic of his fierce-looking image emerging from the holy sacrificial fire to contain and stop Goddess Saraswati and to drive out the demons.

Vaikasi Viszkam in May-June; Aani Thirumanjanam in June-July and Vaikunda Ekadasi in December-January are the festivals celebrated in the temple.

Tit-bits:
12 Vaishnava Azhwars haristore.com
A Divyadesam is one among the 108 Vishnu temples that are mentioned in the works of the  Tamil Azhwar (saints). ”Divya” means “premium” and “Desam” indicates “place” (temple). Of the 108 temples, 105 are in India, one is in Nepal, and last two are believed to be outside somewhere not accessible by us. The shrines are located in the states of Tamil Nadu (85), Kerala (11), Andhra Pradesh (2), Gujarat (1), Uttar Pradesh (4), Uttarakhand (3). Muktinath, Saligramam is the only Divya Desam in Nepal. The 
last two are Thirupalkadal and Paramapadam. Tirupalkaddal is
 the ocean of milk and paramapadam is the Vaikuntha where 
Lord Vishnu presides. The Divya Desams are revered by the 12 Azhwars In the Divya Prabandham, a collection of 4,000 Tamil devotional hymns, the 12 Azhwars mentioned the Vishnu shrines and extolled his virtues.  Divya Desams follow both Thenkalai or Vadakalai traditions. As for temple worships and rituals, invariably most of the Vishnu temples in Tamil Nadu follow 'Thenkalai Samprathayam', Example: Srirangam Ranganathar temple, Triplicane, Chennai Parthasarathy temple. However, pujas are done by priests (Bhattacharyas) belonging to Vadakalai sect in many of the Thenkalai temples.
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http://www.divyadesam.com/hindu/temples/kanchipuram/pavalavannan-temple.shtml
https://en.wikipedia.org/wiki/Divya_Desam