In theory a medieval king was God's representative on Earth, and in some nations kings were literally above the law. In practice, the power of the king was limited by feudal nobles and influential churchmen. A new king had to swear an oath to fulfill the responsibilities of a monarch. The details of this oath varied from one land to another, but included the responsibility to keep the peace, to administer justice and to uphold the law.
The Oath of Kingship
The oath of kingship was one way to remind new kings of their official responsibilities. Newly crowned English kings swore to defend the Catholic Church, maintain peace in the realm, oversee the administration of justice and to uphold any laws chosen by the kingdom. Newly crowned Swedish kings swore to defend the law, rule justly, maintain the peace and serve as the protectors of the poor. The responsibility to maintain the peace and uphold the law eventually led to the development of centralized government and the modern nation-state, but it was a long process.
Keeping the Peace
Kingship in medieval Europe was a very different institution from a modern government, because there was no such thing as an uncontested central authority with power to govern an entire nation. Powerful feudal nobles waged wars and vendettas with each other. Protracted struggles such as the Viking invasions of England and the Hundred Years War between England and France disrupted social order. A king's most important responsibility was to establish order and keep the peace, by force if necessary. This included the duty to fight foreign invaders, to keep the nobles from fighting each other when possible, and to suppress crime and banditry.
The king was responsible for administering justice by resolving disputes between noblemen, appointing officials and presiding personally over major court cases. The king's role in administering justice was so important in medieval society that law and order began to fall apart whenever the king was away from his own land for a long period of time. The nobles relied on the king to resolve their disagreements, because he was the only person they could accept a judgment from without losing face. Therefore, the king's responsibility for administering justice was also part of his responsibility for keeping the peace, notes Nigel Saul in The Three Richards.
Upholding the Law
Throughout medieval Europe, the king was responsible for upholding the law even when he was not bound by it personally. In countries such as France, where the legal system was based on that of ancient Rome, kings were considered the source of all law -- its maker as well as defender -- and were not bound by the law like ordinary mortals. In countries such as England and Sweden, kings were expected to observe established legal practices, such as the Common Law in England, and could not simply create new laws or have subjects arrested on a whim. Even in countries such as France where the king was considered above the law, the king was expected to behave in a morally upright way and any king who failed to do so would have lost his moral authority as the personification of the law, writes Anthony Musson in Expectations of the Law in the Middle Ages.
Some kingly coronation oaths included the responsibility to expand the peace, implying the gradual consolidation of legislative and judicial power of the monarch. Any lord who defied the king could be declared forfeit, losing his lands and his title. Even though it was difficult for any king to control his most powerful nobles, the threat of forfeiture was often enough to compel cooperation. Throughout the Middle Ages, kings used their feudal authority to compel the lords to assist them in battle, to abide by the king's legal judgments and to agree to more and more restrictions on their right to engage in private violence. By the late medieval period, powerful monarchs such as the kings of France had succeeded in creating strong central governments.