It recounts the appearance of the first Shiva linga which pierced the three worlds as a brilliant shaft of light and was witnessed by Brahma and Vishnu
One day Brahma and Vishnu were quarrelling. Brahma claimed, ‘I created the world. I must be God.” Vishnu retorted, “That you seek validation means you cannot be God, “ Then who is God?’ Brahma demanded to know.
As he spoke, a huge column of fire split the earth between them and blazed up through the sky to pierce the highest heavens. Astounded, Brahma and Vishnu decide to determine the source and extent of this brilliant pillar of light. Vishnu became a boar and burrowed deep into the netherworlds. Brahma mounted his goose and flew as far up as the heavens reach.
But even after thousands of years they could not find the bottom or the top of the shaft of light. When they finally give up and returned to their starting place, Shiva emerged from the light in his partial bodily form.
The linga of light is thus the image of the supremacy of Shiva. It is what Mircea Eliade calls the axis mundi or the pillar at the centre of the world, originating deep in the netherworlds, cracking the surface of the earth and splitting the roof of the sky.
In this linga or form, Shiva is not one god among others, but the unfathomable One. This light is the mysterium tremendum which finally cannot be described or comprehended by any or all faces and attributes.
The legend says, the linga of light was the first linga. After that, Shiva vowed that this unfathomable linga would become small so that people might have it as an emblem for their worship.
Wherever, the linga is, there is a tirtha, which in Sanskrit means a shallow ford. Because the linga by nature is a “crossing place” where the worlds are knit together by the shaft of Shiva. ( A tirtha- kshetra means a place of pilgrimage, where one might cross into the other world).
Other deities have idols, images, but only Shiva has the world-spanning form of a linga.
Worship of a shivalingam is considered the prime worship for the devotees of Lord Shiva. Worship of all other forms is considered secondary.
While there are countless Shiva temples throughout India, only a small number of these temples are true places of pilgrimage. It is where Shiva is believed to actually manifested some aspect of his divine nature.
Hindu texts delineate three distinct categories of Shiva shrines: the Jyotir Lingas, the Bhuta Lingas, and the Swayambhu Lingas.
The twelve Jyotir Lingas located throughout the country are considered the most important and are mentioned in the Vedas.
Grineshwar in Visalakam, near the Ellora caves, Maharashtra
Somnath in Saurashtra, Gujarat
• Mahakalaswar at Ujjain, Madhya Pradesh
• Amareswara at Omkareshwar on the river Narmada, Madhya Pradesh
• Tryambakesvara near Nasik on the river Godvari, Maharashtra
• Naganath, in Daruka Vanam, Maharashtra
• Vaidyanath at Deogarh, Bihar
• Bhimasankar northwest of Poona, in Dhakini, Maharashtra
• Kedarnath in the Utterkhand Himalaya, Uttar Pradesh
• Viswanath at Banaras/Varanasi, Uttar Pradesh
• Malikarjuna at Srisailam, Andhra Pradesh state (also a Shakti Pitha site)
• Rameshvaram, Tamil Nadu
The five Bhuta Lingas are places where Shiva is said to have manifested himself as a Linga of a natural element.
• Chidambaram: Ether
• Sri Kalahasti: Wind
• Tiruvanaikka/Jambunath: Water
• Kanchipuram: Earth
• Tiruvanamalai: Fire
The Swayambhu Linga temples contain stone lingas that are believed to have risen up by themselves in the primordial past.
source: Banaras: City of Light – By Diana L. Eck p 107-109.