The Horse
King Sagara was performing the ashvamedha yajna — the horse sacrifice that would establish his sovereignty over the earth. The horse was stolen.
He sent his sixty thousand sons to find it.
The Digging
They searched the earth. Finding nothing, they began to dig — through the soil, through stone, through the layers of the earth. They dug without stopping, destroying everything in their path.
The earth cried out. The gods came to Brahma. Brahma said: this was necessary. What must happen, must happen.
The Finding
Deep at the bottom of the earth, the princes found the sage Kapila — an avatar of Vishnu — in deep meditation, still as a stone. Near him was the horse, placidly grazing.
The princes assumed he had stolen it. They shouted at him. They threatened him. They raised their weapons.
Kapila's eyes opened.
A single glance — a sidelong look from eyes that had been holding the entire cosmos in their vision.
Sixty thousand princes were instantly burned to ash.
The sage closed his eyes and returned to his meditation. The horse stood where it had always stood.
The Consequence
This is the event that made Bhagiratha's tapasya necessary. The ashes of the sixty thousand could not be sanctified without the Ganga — and the Ganga was in heaven.
What followed was Bhagiratha's impossible task: bringing the Ganga down from the sky to the sea to the underworld, to touch the ashes of the sixty thousand and free their souls.