Quis custodiet ipsos custodes?

Quis custodiet ipsos custodes? is a Latin phrase, commonly translated as "Who watches the watchers?", attributed to the Roman poet and satirist Juvenal ((Decimus Junius Juvenalis, 55-127 CE).

Modern liberal democracies try to solve this problem by the principle of the separation of powers. No single group has ultimate power; the executive, legislative, or judicial arms of government all have separate and distinct realms, with interests that often compete and conflict, providing a complex network of checks and balances that prevent power being monopolised by any single group.