Fiat justitia ruat caelum

Fiat justitia ruat cælum is a Latin legal phrase, meaning "Let justice be done though the heavens fall." The maxim signifies the belief that justice must be realized regardless of consequences. According to the 19th-century abolitionist politician Charles Sumner, it does not come from any classical source. It has also been ascribed to Lucius Calpurnius Piso Caesoninus, see "Piso's justice". It was used in the landmark judgment, Somerset v Stewart, where slavery was held to be unlawful at common law.

The falling sky clause occurs in a passage of Heauton Timorumenos, by Terence, suggesting that it was a common saying in his time. In the scene, Syrus suggests a scheme through which Clinia might deceive another into taking actions that would further his love interests. Syrus lays out his plan, while Clinia, who must act it out, finds faults with it, finally asking, "Is that sufficient? If his father should come to know of it, pray, what then?" To which the Syrus replies, "Quid si redeo ad illos qui aiunt, ‘Quid si nunc cœlum ruat?’" — "What if I have recourse to those who say, ‘What now if the sky were to fall?’", the suggestion being that Clinia has no other options available, so to worry that the plan will, obviously, fail if the father finds out makes no more sense than worrying about the fact that it will also fail if the world were to suddenly end.

This concern recalls a passage in Arrian’s Campaigns of Alexander, Book I, 4, where ambassadors of the Celtae from the Adriatic sea, tall men of haughty demeanor, upon being asked by Alexander what in the world they feared most, answered that their worst fear was that the sky might fall on their heads. Alexander, who hoped to hear himself named, was disappointed by an answer that implied that nothing within human power could hurt them, short of a total destruction of nature.

In a similar vein, Theognis of Megara urges "May the great broad sky of bronze fall on my head / (That fear of earth-born men) if I am not / A friend to those who love me, and a pain / And irritation to my enemies." Whereas Aristotle asserts in his Physics, B. IV, that it was the early notion of ignorant nations that the sky was supported on the shoulders of Atlas, and that when he let go of it, it would fall.

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