King John of England sealed Magna Carta at Runnymede in June 1215 under pressure from rebellious barons, establishing for the first time that the king was subject to the rule of law. The document was issued in the shadow of Windsor Castle and was closely tied to the baronial culture of castle-holding and feudal obligation. Though primarily a feudal document, its principles of habeas corpus and legal due process became cornerstones of constitutional government across the English-speaking world.

Magna Carta became a touchstone for poets writing about liberty and tyranny, particularly during the English Civil War and the Romantic era. Milton referenced its principles in his defences of political freedom. Later radical poets including Shelley invoked it as precedent for democratic rights. The association of English castles with baronial resistance gave the document a particular architectural resonance — the castle as bulwark of liberty against royal despotism.