Brahma granted the princes a boon that their cities could only be destroyed by a single arrow when they aligned once every thousand years.
Though Maya intended the cities to be a safe haven, the ambitious princes planned a secret invasion of Devlok, the kingdom of the gods. Ultimately, Lord Shiva, the Destroyer, had to intervene to restore balance. Why It Is a "Hidden Gem" of Indian Animation Tripura (TV Movie 2011) - IMDb tripura- the three cities of maya cartoon network download
Built for the three sons of the fallen Asura king Taraka—Tarakaksa, Kamalaksa, and Vidyunmali—these cities were made of gold (solar energy), silver (lunar energy), and iron/steel (earth energy). Brahma granted the princes a boon that their