Bhairab is one of Lord Shiva's manifestations or another form of Shiva. Lord, Shiva is regarded as guardian of mankind; however, his another form is Bahirav, angry form of Shiva. Bhairav is regarded as destructive incarnation of Shiva.  

Pachali Bairav is in Pachali, a place in Patan (Lalitpur) at the boarder to Kathmandu at the bank of the holy Bagmati River. 

The Jatra is generally held during 4th or 5th day from the start of Dashain festival. This year Pachali Bhairav Jatra is on September 29, 2014 (Ashoj 13, 2071 in Bikram Sambat – Nepali calendar)  

On the night before the main day, a "Kalash" or a holy water vessel bearing the mask of Bhairav is carried to his shrine of Pachali Bhairav, People worship him with prayers, rituals and offerings of meat and Jaad and Raksi (Nepali local liquor). There is a tradition of offering alcohols and liquors (Jaad and Raksi) to Gods in Nepal in Newari culture in Nepal. A priest accompanied by a musical procession brings an image of Shiva’s Son “Ganesh late in the night, an image of his son Ganesh is brought to the temple. 

The "Kalash" is then removed from the shrine and carried on the shoulders of devotees to Durbar Square. In Durbar Square goats and buffaloes are sacrificed to the performers dressed up as Bhairav, Kumari and other deities. Different dances of Bhairav are also performed during the event.

It is said Lord Bhairab gets angry easily the atmosphere at the shrine tends to become highly charged. Buffalo and goat meat and blood are brought to appease him. 

A big feat is organized by people celebrating this festival. Family gathering takes place and people from the same community (guthi) come together to organize the bhoj (feast). People eat baji (chaura in nepali, beaten rice in english) , jaad ( Nepali Liquor), and all other Newari foods during this festival.     

In Nepal, where the tribal substratum is still very visible in the social organization of the Newars, this savge god is probably the most popular and omnipresent of the Hindu Pantheon.

Representations of Bhairav, the terrible aspect of Shiva, are numerous in the Kathmandu Valley, where his cult is very alive and important. Images of Bhairav can be found in Buddhist monasteries as well as in Hindu temples.  Bhairav also dwells in houses, fields, cremation grounds, wells, street-crossings, the four wheels of the chariot of Macchendranath at Patan, and so on.  Bhairav represents impurity, above all the impurity of death. His presence is also believed to have the power to protect the locality around him.

Most of the chronicles explain that it was the Thakuri king Gunakamadev (924-1008 A.D.) who established the worship of Pachali Bhairav. The god is very much associated - at least in the Newari imagination - with the founding of Kathmandu, because it was King Gunakamadev who is traditionally believed to have founded both the city and the festival of Bhairav. He is further credited with bringing the Nava Durga (the goddess worshipped during the festival of Dahsain) to the Kathmandu Valley, starting the festival of Indra Jatra, the Lakhe dances, and so on. He also instituted, reputedly on the advice of the god Karttikeya-Skanda, the ritual conflict - including human sacrifices - that took place between the north (Yambu) and the south (Yangal) of the town during the festival of Sithi-nakha, in order to prevent his subjects from revolting. The political institution of the double kingdom was abolished by 1484, when Ratna Malla made Kathmandu his kingdom, but some of the associated rituals and social structures remain. The Kings of Patan were involved in the annual festival of Pachali Bhairav and a puja tray is still sent in his honor to the temple by their descendants, living in Mangal Bazaar at Patan, who are called Bhairav Malla.

One of the most ancient temples of Bhairav in Kathmandu is situated in the south of the modern town near Tekudovan at the confluence of the Bagmati and Vishnumati rivers. It is very close to the cremation ghat on the Bagmati, the Ganga of the Kathmandu Valley. Under the shade of a big pipal tree, on the altar of the open sanctuary, there is a stone representing Pachali Bhairav, with surrounding stones that symbolize his attendants (gana). Facing the altar is the betal on which blood sacrifices are performed. Because of the similarity of the Pachali Bhairav stone to the human buttocks, people coming from the plains of India made fun of the sacrificial practices of the Newar. So in the 17th century, King Pratap Malla covered most of the original emblem and now only a section of the stone is visible.

According to legend, Pachali Bhairav was the king of Pharping (a town to the south of Kathmandu), and had the habit of locking himself in a room of his palace to eat enormous quantities of rice and a goat at one sitting. One evening, his wife insisted upon coming and sharing his meal. The king accepted but informed her that he would have quite another appearance, and that she would have to throw some grains of rice on him in order to restore his human aspect. When she saw his true form, his wife was so terrified at the sight of Bhairav that she ran away, forgetting to throw the grains. Afraid of being discovered by his subjects, the exposed king took refuge in the place where the temple of Pachali Bhairav stands today. His wife stumbled a little further on and became Lumarhi, the dangerous goddess Bhadrakali whose temple stands at the edge of the Tundikhel field. 

In another version, Pachali Bhairav had the habit of leaving Pharping each morning to bathe in the Ganga at Banaras and returning to Kathmandu in the form of a handsome man. In this way, he seduced a young girl of the butcher caste (kasai) who tended pigs near the temple site. (In some accounts, he was instead a jyapu [farmer] who thus broke the rules of caste.) Before long, she too became curious and he finally agreed to reveal himself, provided she threw some grains of rice as soon as she saw his real identity. She too forgot and fled as soon as she was confronted by her grotesque lover. Bhairav pursued her through the night, but when day began to dawn he sought to hide himself. He reached a cremation ground and wrapped a bamboo mat, such as the Newars use for their dead, around himself. This one had in fact been used to bring a corpse to the cremation ghat. He didn’t have enough time to disappear totally underground - the stone venerated today is his unconcealed buttock! Another version explains the close relationship of the Kasai caste with the god Ganesh. The seduced butcher girl became pregnant and her fear at the grotesque appearance of her lover provoked the premature birth of the child, who was adopted by the Kasai. The child is none other than Ganesh, who is venerated by the butchers of South Kathmandu in the form of a small bronze statue attached to a drum that they play during different ceremonies.

There is yet another account in which Bhairav was not a king but a farmer: Bhairav walked with his daughter Kumari and his son Ganesh during the festival of Indra. Bhairav’s wife, Ajima (also of Jyapu caste) was jealous because she was not with them, and asked Bhairav to stroll with her around Kathmandu. He agreed, but not during the Indra Jatra. That is why during the Pachali Bhairav festival, a procession is held where a man chosen to wear the mask of Bhairav and another person wearing the mask of  Ajima walk together through Kathmandu. During Indra Jatra, the procession of Kumari the virgin-goddess is in fact accompanied by Ganesh and Bhairav, but in this context, Bhairav (like Ganesh) is represented by (and believed to be embodied in) a small boy of the Buddhist Shakya caste. The boy’s Shakya family regularly sends a tray of offerings to the temple of Pachali Bhairav, mirroring the practice of the Kings of Patan.

Despite his supreme position in a number of tantric schools of Shaivism, Bhairav seems at first sight to have a modest place beside the other gods of the Hindu pantheon. But in Nepal, where the tribal substratum is still very visible in the social organization of the Newars, this savage god is probably the most popular and omnipresent of the pantheon. Among his unique manifestations, Pachali Bhairav is not only the most important but also the one which best illustrates the indigenous character of his worship and his penetration into Nepali culture. His temple, beside a cremation ground on the Bagmati River, is frequented most by twelve families of Hindu farmers (and earlier by Buddhist oil-pressers) living in the southern part of Kathmandu, for whom he serves as the clan deity. The annual Bhairav festival, celebrated during Dashain, provides the occasion for the transfer of the vessel of Pachali Bhairav (which he has been invoked to inhabit) from one farmer family to the next, and also requires the specialized participation of members of several Buddhist castes.

The first reference to Pachali Bhairav is an inscription from 1333 A.D. that was discovered in the Maru Sattal or Kashthamandap at the center of Kathmandu. This wooden building, which marked the northern boundary of Yangal, seems to have been the royal council chamber and the temple of Pachali Bhairav. In the inscription, the god is invoked as witness to a political treaty and as the guardian of certain funds deposited as a pledge to this temple. Towards the beginning of the twelfth century, this entire section of the city was also called Kashthamandap, from which is derived the modern name of the city, Kathmandu. In 1379, King Jayasthiti Malla gave this Sattal to the Nath ascetics connected with the worship of Bhairav. Their descendants, the Kapalikas or Kusle Yogins, continued to live there until recently (1966), when they were turned out so that restoration of the building could be begun. The Kashthamandap still provides shelter today for a statue of Gorakthnath and is still associated with the worship of Pachali Bhairav. Current customs among the Buddhist Newars of Kathmandu indicate that the building had also probably previously had Buddhist associations.

Jyapu farmers in Kathmandu, who still represent a third of the population of the old town, are spatially distributed in four sectors, each associated to a particular temple: Swayambunath (Simbu) and Lutimaru Ajima at the north and west, Bhadrakali at the south-east and Pachali at the south. The principal devotees of Pachali Bhairav are farmers and oil-pressers who live in the southern part of Kathmandu. At the daily level, the farmers are the most involved because they maintain the open-air temple. The tantric priest (Achaju) who performs the daily rituals is none other than the eldest male member (Thakali) of the family currently in charge of the open-air temple. The daily rituals are performed morning and evening by the farmer guardians and by a Newari Buddhist “brahman” Vajracharya priest. They offer, among other things, eggs, goats, and above all poultry to Pachali Bhairav, but the animals are never sacrificed on the altar itself but only on the betal. Special rituals are also celebrated on the eighth day of Dashain (Maha-Ashtami) and on Pachare or Pishacha-chaturdashi, a three-day festival beginning on the fourteenth day of the dark fortnight of the month of Chaitra (March-April). 

The origin of Bhairav can be traced to the conversation between Lord Brahma and Lord Vishnu recounted in "Shiv Maha-Puran" where Lord Vishnu asks Lord Brahma who is the supreme creator of the Universe. Arrogantly, Brahma tells Vishnu to worship him because he (Brahma) is the supreme creator. This angered Shiva who in reality is the creator of all. Shiva, then incarnated in the form of Bhairava to punish Brahma. Bhairav beheaded one of Brahma's five heads and since then Brahma has only four heads. When depicted as Kala Bhairab, Bhairab is shown carrying the decapitated head of Brahma. Cutting off Brahma's fifth head made him guilty of the crime of killing a Brahmin, and as a result, he was forced to carry around the head for years and roam as Bhikshatana, a mendicant, until he had been absolved of the sin.

In another version, when Brahma sees the cosmic confusion while creation of universe and ponders how to settle it. He created Saraswati from his imagination ('Manasaputri'). She issued as Shatarupa. She presented him with the wealth of knowledge and wisdom. But Brahma was infatuated with her beauty and pursued her. He sprouted a fifth head to gaze at her continuously. The horrified goddess took multiple forms to escape his eye, but Brahma continued to take a complementary form and chase her. This unlawful lust caused an imbalance in the universe and Lord Shiva took the form of Bhairav to put an end to such incest. He confronted Brahma and cut off his fifth head which brought him to his senses. He then performed a yagna to purify himself, reciting mantras with his four heads for salvation.

In the form of the frightful Bhairava, Shiva is said to be guarding each of these Shaktipeeths. Each Shaktipeeth temple is accompanied by a temple dedicated to Bhairav.