TheCatherion Imprimiture was the experiment, undertaken during theImperator Presidency, that resulted in the creation of a new generation ofcasts called "babels".

To create the babels, abreeding-engine was symbolically purchased from the extinctHouse Catherion for the price of threebirds'eggs, a small plot of land, and a smallpocket watch immaculately crafted byMr Harrison ofYorkshire around1765. During the experiment, grotesque modifications were made to the breeding-engine.

The experiment lasted for fifty years, during which at least three and at most eight babels were grown. Many or all of the babels were incurably insane;one escaped and brutally slaughtered the inhabitants of House Catherion. At the time of the massacre, the pocketwatch disappeared fromthe Homeworld. By the time of theWar in Heaven, the "receipt" of the breeding-engine's purchase was the only surviving documentation of the CatherionImprimiture or the babels. (PROSE:The Book of the War)