As one of the most fundamental tools for managing the Mongol Empire, the operation of the Yam system was regulated by the written law Yassa. Both messengers and station operators enjoyed extended privileges. Even for everybody else, the requirements of the Yam took precedence before their other duties and interests, and they had to support it whenever it became necessary. This kind of support was made possible by the strict discipline within the empire, which also led to a high level of security, often described as Pax Mongolica.