Magna Carta is the most famous document in English history. And yet its survival is purely accidental. King John, who negotiated the document with his rebellious barons, had no intention of honouring its contents. Annulled by the pope within weeks of being issued, it was destined to oblivion. But with the sudden death of John, all of this changed. Magna Carta was reissued by the regents of the boy King Henry III as an apology for past misrule and...