The Burning of the Three Cities

Among the tales the sages told the Pandavas was the story of the burning of the Three Cities - how the great god Shiva destroyed three impregnable flying fortresses with a single arrow, and why even that one arrow needed the strength of all the gods behind it.

It began with three asura brothers, sons of a great demon, named Tarakaksha, Kamalaksha, and Vidyunmali. Like their kind, they hungered for power that no one could take from them, and to win it they went away and performed penances of extraordinary severity, standing in austerities for age upon age, until the heat of their discipline compelled the Grandfather of the worlds, Brahma, to appear before them and offer a boon.

The three brothers asked, as such beings always do, for invulnerability - for fortresses that no enemy could ever destroy. And Brahma, bound to reward their penance, granted them a boon of a strange and cunning kind: cities that would be all but impossible to bring down, protected by a condition so nearly unmeetable that the brothers believed themselves safe forever.