The Sacred Ganga Talao - Mauritius

During the Vedic period, both Vishnu and Shiva (as identified with Rudra) played relatively minor roles, but by the time of the Brahmanas (c. 1000-700 BCE) both were gaining ascendance.^[166] By the Puranic period both deities had major sects that competed with one another for devotees.^[167] Many stories developed showing different types of relationships between these two important deities.

Sectarian forces each presented their own preferred deity as supreme. Vishnu in his myths "becomes" Shiva.^[168] The Vishnu Purana (4th c. CE) shows Vishnu awakening and becoming both Brahmā to create the world, and Shiva to destroy it.^[169] Shiva also is viewed as a manifestation of Vishnu in the Bhagavata Purana.^[170] In Shaivite myths, on the other hand, Shiva comes to the fore and acts independently and alone to create, preserve, and destroy the world.^[171] In one Shaivite myth of the origin of the lingam, both Vishnu and Brahmā are revealed as emanations from Shiva's manifestation as a towering pillar of flame.^[172] The Śatarudrīya, a Shaivite hymn, says that Shiva is "of the form of Vishnu".^[173] Rivalry between the two sects is apparent in the story of Śarabha (also spelled "Sharabha"), the name of Shiva's incarnation in the composite form of man, bird, and beast. Shiva assumed that unusual form to chastise Vishnu in his hybrid form as Narasimha, the man-lion, who killed Hiranyakashipu, an ardent devotee of Shiva.^[174][175]

Syncretic forces produced stories in which the two deities were shown in cooperative relationships and combined forms. Harihara is a the name of a combined deity form of both Vishnu (Hari) and Shiva (Hara).^[176] This dual form, which is also called Harirudra, is mentioned in the Mahabharata.^[177] An example of a collaboration story is one given to explain Shiva's epithet Mahābaleśvara, "Lord of Great Strength" (Maha = great, Bala = strength, Īśvara = Lord). This name refers to story in which Rāvaṇa was given a linga as a boon by Shiva on the condition that he carry it always. During his travels, he stopped near the present Deoghar in Bihar to purify himself and asked Narada a devotee of Vishnu in the guise of a Brahmin to hold the linga for him, but after some time Narada put it down on the ground and vanished. When Ravana returned, he could not move the linga, and it is said to remain there ever since.^[178]

REFERENCES:  http://en.wikipedia.org/wiki/Shiva