In 1215, the nobles of England, chafing under King John's excessive taxation and arbitrary justice, would only renew their oaths of fealty if John agreed to their demands. John was forced to agree, and all parties signed the Magna Carta in June of that year.
Its signing was a pivotal moment in human history. The Master sought to prevent its signing, thus altering the course of history, in ways that were never clearly revealed. He was prevented from doing so by the Fifth Doctor. (TV: The King's Demons)
On 23 November 1963, the Fourth Doctor offered his granddaughter Susan Foreman's best friend Debbie the opportunity to travel with him and see the signing of the Magna Carta but she declined. (PROSE: Those Left Behind)