"Fiat justitia, et pereat mundus" is a Latin phrase. It means: “Let there be justice, though the world perish.”
It was the motto of Ferdinand I, Holy Roman Emperor,[1][2][3] probably originating from Johannes Manlius’s book Loci Communes (1563), and it characterizes an attitude, which wants to provide justice at any price. It is actually about half a century older than its first documented use in English literature.
A famous use is by Immanuel Kant, in his 1795 Perpetual Peace (Zum ewigen Frieden. Ein philosophischer Entwurf.), to summarize the counter-utilitarian nature of his moral philosophy, in the form Fiat justitia, pereat mundus, which he paraphrases as "Let justice reign even if all the rascals in the world should perish from it".[4][5][6]
The phrase has not been traced to Classical Rome and may first appear in Johannes Manlius’s book Loci Communes.