Magna Carta (1215)

Sealed by King John of England in 1215 under pressure from rebelling barons, the Magna Carta (Great Charter) established for the first time that the king was subject to the rule of law and not above it. Its most enduring clauses — protecting subjects from arbitrary imprisonment and guaranteeing access to justice — became foundational to constitutional law across the English-speaking world and beyond. A seminal ancestor of every modern legal instrument that constrains state power and protects individual rights.