Founding Documents: Magna Carta

Magna Carta was sealed on a field in England in 1215. It's purpose was to appease some frustrated Barons, and it was never intended to last. Over 800 years later, this document is credited with establishing one of the most foundational principles of our democracy. So what does Magna Carta actually say? And how did it get from dubious stalling tactic in the 13th century to U.S. Supreme Court arguments in the modern era?