The landmark event that occurred in 1215 in English history and governance was the signing of the Magna Carta. This document was significant because it established the principle that everyone, including the king, was subject to the law. The Magna Carta introduced foundational rights for nobles and laid groundwork for the development of constitutional governance. It curtailed the absolute power of the monarchy, leading to the emergence of legal frameworks, due process, and the concept of trial by jury. This event is celebrated as a pivotal step in the evolution of democratic principles.