The War of the Keys: The History and Legacy of the Military Conflict Between the Holy Roman Empire and the Vatican

It has been famously pointed out that the Holy Roman Empire was neither holy, nor Roman, but it was also not an empire in the sense people expect when hearing the term. In theory, the emperor was the highest prince in Christendom, and his dominion extended the length and breadth of Western Europe. The empire had been created by the papacy when Pope Leo III famously crowned the supposedly unwitting Charlemagne in Saint Peter’s Basilica, intending to recreate the Western Roman Empire. In truth, the imperial power did not extend beyond central Europe, which by the beginning of the 16th century included Germany, northern Italy, and the Netherlands. Even in these lands, however, the emperor struggled to command obedience. His dominion over northern Italy was theoretical only, the cities of the Netherlands were deeply conscious of their ancient rights and privileges, and Germany had long ceased to be compliant. The latter had become a collection of principalities, dukedoms and bishoprics which vied with each other and pursued their own agendas. They were, however, united in only one sense: denying the emperor power and resisting attempts to centralize the government.
At the same time, the secular sovereigns frequently butted heads with religious authorities back in Rome, and these conflicts took place over the course of several centuries. For example, in the 11th century, the tensions between the Holy Roman Empire and the Church over the power to invest bishops with authority led to decades of civil war in Germany on the way to establishing the relationship between Church and state, elevating the status of the papacy and weakening the Holy Roman Empire. But it was not until the 13th century that the conflicts actually took on a military nature.

What is crucial in understanding the conflicts is to not view them with the benefit of hindsight. Most importantly, no nation as people recognize it today yet existed, as England, France, Germany, and Italy were largely geographical expressions, not national identities. Western Europe was based on feudalism, and society was structured around personal relationships rather than national characteristics. Members of a feudal system swore fealty to a superior, in exchange for land or protection. At the top of the pyramid was the king, deemed to be God’s representative. He apportioned land to the great nobles, and they vowed their obedience and arms to him. In turn, the nobles established similar contracts with lower vassals. At the bottom of the feudal pyramid were the landed peasants and the landless serfs, who paid for protection in the form of material tribute and labor. Thus, society was divided into three estates, or orders: the nobility, clergy, and commons. The nobility was the ruler and warrior class, and the commons consisted of peasants and townspeople.

The clergy occupied a privileged place in medieval society. Europe had inherited Christianity from the Roman Empire, and the concept of a united Christendom and empire were practically synonymous. Indeed, there was no real consciousness of the Roman Empire ever having ended. After the Western Roman Empire collapsed in the late 5th century, the Germanic rulers of Western Europe continued to recognize the Eastern Emperor in Constantinople until Charlemagne, and after the dissolution of the Frankish Empire, the imperial seat was transferred to Otto I, King of East Francia in modern Germany.

By the late 10th century, however, the emperor’s reach was rarely felt beyond Germany and northern Italy, and the question of who was supposed to be the imperial head was unresolved. The emperor claimed rights over both church and state, while the pope, who placed the crown on the emperor’s head, asserted his supremacy over all princes, even the emperor. The tensions set the stage for civil conflicts to spill over into violence, which is eventually what happened.