Shilada underwent severe penance to have a boon– a child with immortality and blessings of Lord Shiva, and received Nandi as his son. It is said that Nandi was born from a Yajna performed by the Shilada, and his body was clad in armour made out of diamonds, when he was born. Nandi grew as an ardent devotee of Lord Shiva and he did penance to become his gate-keeper, as well as his mount, on the banks of river Narmada, near Tripur Tirth Kshetra in present-day Nandikeshwar Temple, in Jabalpur, Madhya Pradesh. Nandi got the divine-knowledge of Agamic and Tantric wisdom taught by Shiva, from goddess Parvati. He could teach that divine-knowledge to his eight disciples, who are identified as the progenitors of Nandinatha Sampradaya, namely, Sanaka, Sanatana, Sanandana, Sanatkumara, Tirumular, Vyagrapada, Patanjali, and Sivayoga Muni. These eight disciples were sent in eight different directions of the world by Nandi, to spread this knowledge. Many other puranic tales are available about Nandi. One describes his conflict with Ravana, the antagonist of Ramayana. Nandi cursed Ravana (the demon King of Lanka), that his kingdom would be burnt by a monkey (Vanara). Later, Hanuman burned Lanka when he went in search of Sita, who was imprisoned by Ravana in Ashok Vatika. Tamil "Thiruvilaiyadal Puranam" mentions another story in which Nandi is incarnated as a whale. It says that Parvati lost her concentration while Shiva was explaining the meaning of "Vedas" to her. Parvati, then incarnated as a fisher-woman to atone. To unite his master and his beloved-wife, Nandi took the form of a whale and started to trouble the people. Fisher-woman Parvati's father told, that one who would kill the whale would marry his daughter. Later, Shiva took the form of a fisherman and killed the whale, and received Parvati in her previous form. "Agamas" describe him in a zoo-anthropomorphic form, with the head of bull and four hands, with antelope, axe, mace, and abhayamudra. In his mount form, Nandi is depicted as a seated bull in all Shiva temples, all over the world.