Stock Photo - King John (1167-1216) signing the Magna Carta at Runnymede, 1215. The Magna Carta was the most significant early influence on the extensive historical process that led to the rule of constitutional law today. Magna Carta influenced many common law and other documents and is considered one of the most important legal documents in the history of democracy. It was originally written because of disagreements between Pope Innocent III, King John and the English barons about the rights of the King. Magna Carta required the king to renounce certain rights, respect certain legal procedures and accept that his will could be bound by the law. It explicitly protected certain rights of the king's subjects, whether free or fettered - most notably the right of Habeas Corpus, meaning that they had rights against unlawful imprisonment.