Quis custodiet ipsos custodes?

Quis custodiet ipsos custodes? is a Latin phrase found in the work of the Roman poet Juvenal from his Satires (Satire VI, lines 347–348). It is literally translated as "Who will guard the guards themselves?", though it is also known by variant translations.

The original context deals with the problem of ensuring marital fidelity, though it is now commonly used more generally to refer to the problem of controlling the actions of persons in positions of power, an issue discussed by Plato in the Republic. It is not clear whether the phrase was written by Juvenal, or whether the passage in which it appears was interpolated into his works.

The phrase, as it is normally quoted in Latin, comes from the Satires of Juvenal, the 1st/2nd century Roman satirist. Although in its modern usage the phrase has universal, timeless applications to concepts such as tyrannical governments, uncontrollably oppressive dictatorships, and police or judicial corruption and overreach, in context within Juvenal's poem it refers to the impossibility of enforcing moral behaviour on women when the enforcers (custodes) are corruptible (Satire 6.346–348):

audio quid ueteres olim moneatis amici,
"pone seram, cohibe." sed quis custodiet ipsos—
custodes? cauta est et ab illis incipit uxor.

I hear always the admonishment of my friends:
"Bolt her in, constrain her!" But who will guard
the guardians? The wife plans ahead and begins with them.

Modern editors regard these three lines as an interpolation inserted into the text. In 1899 an undergraduate student at Oxford, E.O. Winstedt, discovered a manuscript (now known as O, for Oxoniensis) containing 34 lines which some believe to have been omitted from other texts of Juvenal's poem. The debate on this manuscript is ongoing, but even if the verses are not by Juvenal, it is likely that it preserves the original context of the phrase. If so, the original context is as follows (O 29–33):

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