Tripura: Three Cities, Three Illusions
One arrow, three bodies undone
Three asura brothers receive three flying cities, one of gold, one of silver, one of iron, and a boon that makes them invincible as long as the three cities do not align. They become unconquerable for a thousand years. Shiva waits for one moment when the three align, draws a single arrow, and fires.
Three Brothers, Three Boons, Three Cities
Long after the great churning of the ocean, in a stretch of cosmic time when the asuras and devas were still arguing over who had the better claim to the universe, the demon Taraka had three sons. Tarakaksha, Vidyunmali, and Kamalaksha. They were brothers in the way only asura brothers can be in the Puranas, perfectly aligned, perfectly disciplined, and perfectly committed to a goal the gods would later regret allowing.
They went into deep tapas. Years passed. The mountains they sat on began to look slightly different from the weight of their stillness. Brahma, eventually, came to grant a boon.
The brothers had thought carefully. They knew the standard asura mistake. Asking for immortality outright was always refused. Asking for protection from a single named god could be circumvented. So they crafted their boon as a riddle.
"Build us three cities. One of gold, one of silver, one of iron. Place them in the sky, in the air between earth and sky, and on the earth. Let them move freely. Let them be invincible from every weapon, every god, every direction, except one. Let our death come only from a single arrow that strikes all three cities at the same instant, when they happen to align in a single line, and only that."
Brahma, who had to honour the discipline of their tapas, granted it. He warned them, gently, that the alignment of three flying cities into a single straight line was a thousand-year event. They would, by any practical measure, be immortal.
The brothers laughed.

The great architect Maya, the asura craftsman, built the three cities. Saubha of gold rode high in the sky. Saubha of silver floated in the air. Saubha of iron rolled on the earth. The cities were each enormous, full of palaces, gardens, libraries, war-chambers. The brothers ruled them. From the protection of the three cities, they began, slowly, the work that all asuras eventually do. They troubled the gods. They troubled the rishis. They troubled the worlds.