“Behind them all, carried upon the bed of an enormous carriage with thirteen sets of iron-banded wheels, nestled within a casement crafted from the bronzed skull of a giant, was the holiest relic in all skavendom: the Black Ark, the compact between the Horned Rat and the first Seerlord. Imprinted upon a block of purest warpstone, its quality unsurpassed by the richest ores ever found, were the thirteen tyrannies, the sacred dictates by which the skaven might placate their terrible god and achieve the promise He had made to them: that one day the ratkin would inherit the whole of the world.”
Book:Wolf of Sigmar