The Breaking of Chains

The legend of what will happen if Fortis, The Chained every breaks free from his chains that Barbossa, The Sunlord confine him within the elemental sphere of fire. away from Bavo'sand and in such a place that his followers would never be able to retreive him.
The prophecy says that if Fortis breaks free the world will come to an end, as he brings fire and darkness to the city and lands, destroying all in a fit of rage against his brother's creation, to enact revenge for his exile millenium ago. It mentions Twins of Purple Eye and the destruction and terror of what comes after.
The prophecy came from Rani Graen ramblings, who was inflicted by the Darkness of Vitale in the early days of the republic, she prophecies many things including the Crystal Tower and the Fall of the Noble houses.

in the days before the end, the sister will appear in the sky in a deep purple.
The Twins of Purple Eyes will break the Chains of the Chained one
The Darkness unchained bring destruction to his brothers design.
Fire and Darkess will cover the great city and he would rule above the destruction.
He and his kind will hunt the living.
The world will Crack and Shadows will spread across the lands

— Rani

Some of the prophecies of Rani have come true others like this one have not yet, Who knows if there is any truth to it. Copies of these prophecies are restricted within the city, and while some of the Noble houses almost certainity Graen, the only complete copy known of is the one that stored within the Crystal Tower.