Item from The Wheel of Time by Robert Jordan
Seven discs of cuendillar that anchor Lews Therin's patch on the Dark One's prison — they've been weakening for three thousand years, and when the last one breaks, the Last Battle begins.
Lews Therin sealed the Dark One's prison with seven seals of cuendillar, placed at strategic points in the Pattern. For three thousand years, they held. Then they started breaking — slowly at first, then faster as the Last Battle approached. Each broken seal weakens the prison further, allowing more of the Dark One's influence to leak into the world. Rand's plan required breaking the remaining seals intentionally — removing Lews Therin's flawed patch so he could create a new, permanent seal. This was the most controversial decision of the Last Battle: deliberately weakening the prison in order to repair it properly.
Small discs of cuendillar — heartstone, the hardest substance in existence — each inscribed with the ancient Aes Sedai symbol (the yin-yang-like double teardrop). They were once indestructible; their gradual breaking is evidence of the Dark One's growing power. They crack like porcelain when they fail.
Also known as: the seals, the Seals on the Dark One's Prison