Nag Nathaiya is a festival of Varanasi. Nag Nathaiya festival is a part of the Krishna Leela ceremony, a mythological tradition involving depiction of a famous episode in the life of lord Krishna. The Nag Nathaiya festival of Varanasi is held at the Tulsi Ghat. The Nag Nathaiya festival is famous as Nag Nathaiya Leela. The festival celebrates Krishna's conquest of the serpent Kaliya. The Nag Nathaiya festival is held on the fourth tithi of Kartik's light fortnight, Paksha; which is usually sometime between November and December.
This festival was started by Tulsi in the 16th century at Tulsi Ghat. The legend of Nag Nathaiya festival can be traced back to the time of Mahabharata. According to an episode of Mahabharata, one day Lord Krishna while playing with his friends lost his ball in the river. When all began asking for the ball little Krishna dived into the river to fetch it back. He dived down deep inside the river. There he was confronted by the poisonous King Cobra, Kaliya. He was feared by the villagers for the terror he spread in the village. The battle went for long but soon Kaliya Nag recognized the strength and power of Lord Krishna. He bowed his head in front of the Lord and promised not to hurt the villagers residing in the village. The snake lifted Lord Krishna on its head and took him to the surface. On the other hand, Krishna's friends became worried as it had been a long time that he went down in the river. Thus the friends were delighted upon seeing him back. It is said that Lord Krishna not only defeated the cobra but also purified the water and the air of the poison that was spread by the nag. The entire episode has since been known as `Krishna Lila` or Krishna's magical charm.
When The festival celebrating Krishna's victory is reenacted at Tulsi ghat, a large branch of Kadamba tree is planted at the edge of the river Ganga and the young boy acting as Krishna- who functions in this context not as a mere actor, but as the embodied from (svarup) of Krishna- jumps from the tree branch into the river, where an effigy of kaliya lies in wait. The child embodying Krishna climbs onto the effigy's head and strikes a flute playing pose. Propelled by human assistants, the serpent effigy along with the boy Krishna on its head make a circular sweep in the water, parading in front of thousands of spectators, who watch the display from the river bank or from boats floating on the Ganges waters. The festival is attended by Kashi Naresh (the titular king of Varanasi) every year who views the Leela from royal boat. Later he gives awards to the actors performing in Leela.