Janamejaya started Sarpa-satra, Sarpa-yajna to avenge the death of his father, Raja Pariskhit.
Prikshit was killed by the serpent, Takshaka.
Janamejaya would have the entire Naga-vamsha wiped out.
In addition to that, the serpents’ own mother had cursed them to perish in fire.
The curse was also approved by Brahmaji because the serpents had multiplied into crores by that time.
Without reason, they have been attacking and killing innocent people.
Their number was to be controlled.
Sarpa-yajna was the most efficient way to do it.
Being a yajna and not just killing, Janamejaya will be free from karmic responsibilities.
The rare Vedic ritual for this was Sarpa-yajna.
Who were the purohitas of Sarpa-yajna?
Not ordinary.
Great Maharshis they were.
The Hota , the Rigvedi-purohita, was Chandabhargava.
He belonged to Sage Shaunaka's own vamsha.
He was very famous.
Mahabharata is being narrated to Shaunaka and the other Rishis in Naimisharanya.
The Yajurvedi-purohita was Pingala.
The Yajurvedi-purohita of yajna is called Adhwaryu.
That is the title.
The Samavedi-purohita, Udgata was Kautsa.
He was very senior and very learned.
The Brahma who supervises the entire yajna, the Atharvavedi-purohita, was Jaimini.
Not just these four, they were the chief purohitas.
Sage Vyasa himself participated in Sarpa-yajna along with Shukadeva and all his disciples.
Also great Rishis such as-
उद्दालकः, प्रमतकः, श्वेतकेतुः, असितः, देवलः, नारदः, पर्वतः, आत्रेयः, कुण्ठः, जठरः, द्विजः, कालघटः, वात्स्यः, श्रुतश्रवा, कोहलः, देवशर्मा, मौद्गल्यः, समसौरभः
and many more.
The very fact that these Rishis participated in the Sarpa-yajna justifies its cause.
They know dharma inside-out.
As Brahma had explained, Sarpa-yajna’s real purpose was to contain the number of vicious serpents.
Billions of serpents perished in that yajna.
Purohitas would make an offering in the form of an ahuti in Agni and call out a serpent's name or even names in groups.
They will all fall into the fire and burn to death.
They are pulled into the fire by mantra-shakti.
Some of the prominent serpents who died during sarpa yajna were: from Vasuki's vamsha
कोटिशः मानसः पूर्णः शलः पालः हलीमकः पिच्छलः कौणपः चक्रः कालवेगः प्रकालनः हिरण्यबाहुः शरणः कक्षकः कालदन्तकः
From Takshaka's clan
पुच्छाण्डकः मण्डलकः पिण्डसेक्ता रभेणकः उच्छिखः शरभः भङ्गः बिल्वतेजा विरोहणः शिली शलकरः मूकः सुकुमारः प्रवेपनः मुद्गरः शिशुरोमा सुरोमा महाहनुः
From the vamsha of Airavata -
पारावतः पारिजातः पाण्डरः हरिणः कृशः विहङ्गः शरभः मेदः प्रमोदः संहतापनः
From the vamsha of Kauravya
एरकः कुण्डलः वेणी वेणीस्कन्धः कुमारकः बाहुकः शृंगवेरः धूर्तकः प्रातरः आतकः
From thee clan of Dhritarashtra
शङ्कुकर्णः पिठरकः कुठारमुखः सेचकः पूर्णाङ्गदः पूर्णमुखः प्रहासः शकुनिः दरिः अमाहठः कामठकः सुषेणः मानसः अव्ययः भैरवः मुण्डवेदाङ्गः पिशङ्गः उद्रपारकः ऋषभः वेगवान् पिण्डारकः महाहनुः रक्ताङ्गः सर्वसारङ्ग्ः समृद्धः पटवासकः वराहकःवीरणकः सुचित्रः चित्रवेगिकः पराशरः तरुणकः मणिः स्कन्धः अरुणिः
See the kind of detailing.
It is not that billions of Nagas perished.
These are all real incidents, you see.
In order not to fall into the fire, the serpents would hold on to whatever they found or hold on to one another.
But, nothing could save them.
All kinds of poisonous snakes, in billions.
Some miles long, huge.
Some tiny.
Of different colors: black, blue, red, green.
Their burning bodies filled the air with a bad smell.
Hundreds of rivers of snake fat flowed out of the homa kunda as the snakes' bodies burned.
They were falling in thousands from the sky into the homa kunda.
Takshaka got scared.
He rushed to Indra.
Indra said, I will protect you, you be here, in my palace.
I will protect you.
Vasuki, the king of serpents, got worried.
There were a few left.
Brahma's words that only cruel serpents would die, are they still valid?
It looks like the whole Naga-vamsha, including himself, was going to perish.
He called his sister, Jaratkaru.
The time has come to send your son Astika to the sarpa yajna venue and stop it somehow.
According to Brahma, Astika is the only person who can stop the Sarpa-yajna.