Dominium mundi is the idea of universal dominion developed in the Middle Ages. Inspired by the memory of the Roman Empire, dominium mundi implied the recognition of one supreme authority, which generated a prolonged political and spiritual struggle between imperial and ecclesiastical power. This struggle can be said to have begun with the Investiture Controversy, and was mainly embodied by the Holy Roman Empire and Catholic Church, which elevated the emperor and the Pope, respectively, to the status of supreme ruler.

The idea of universal dominion divided Italy into the warring faction of Guelphs and Ghibellines. Guelphs supported the Church, while the Ghibellines supported the Empire. After two hundred years of division during the 12th and 13th centuries, neither one of the powers had prevailed, due to their mutual dependency and the rise of the powerful and practically independent reigns of Church and the State. The idea of dominium mundi did not reappear in its original form, despite the fact that both universal powers subsisted.

During the reign of Frederick I (1152–1190), the imperial idea had already reached maturity. Its continuity was emphasized in Europe from the Roman times, through the link to the Carolingian Empire. In fact, Frederick I spoke about Charlemagne as the model of emperors and had him canonized in 1165 without the requirements. The thesis on the public sovereignty that Roman law (rediscovered by the European jurists and politicians in the twelfth century) has were also used in favor of the imperialist ideals. It was of them that it was deduced the oneness and the universal character of the Holy Roman Empire, considered "a project of worldwide dominion" that symbolized the whole period. Given these premises, it was believed in the court of Frederick I that the Empire, was sacred as it was established directly by divine will to act as a form of political organization for humanity. The expression Sacrum Imperium appears for the first time in a document of 1157.

Notwithstanding, it cannot be forgotten that the 12th century saw the beginning of the revitalization of the monarchic power over feudalism, after several centuries of deep decay of royal authority. The Empire did not stay at the margin of this evolution instead recovering strongly its prestige. Nevertheless, it was badly managed, causing important consequences for the political future of the territories of Germany and Italy. The reconstruction of the monarchies also went against the projected Dominium Mundi. Because of this, Frederick I, as well as his son and successor Henry VI, tried to conciliate both events imagining a universal temporal empire, at whose front was an emperor with supreme authority, superior to the power of various kings, called "régulos" or "local kings". This supreme authority seemed necessary, because it was believed that the Empire was the way to maintain unity in Christianity in preparation for the end times. Without considering this eschatological and messianic element, one cannot correctly understand what the Empire meant for the men of the time, in particular for emperor Frederick I.

The foundations of the ecclesiastical vision can be exemplified by these sources:

In the 12th and 13th centuries the rediscovery of old Roman law and the ordenación of the canon law sparked a new era for the legal ordering of the western world. This deeply influenced the politics of the time, especially in the course of the struggle of the Dominium Mundi between the Empire and the Pontificate. The Roman law known by the medieval Europe was exclusively the compilation made by the emperor Justinian in the 6th century, which consists of several differentiated parts:

Of all these, the one of greatest influence in the medieval rediscovery was the Digest. The Justinian work would, starting in the 16th century, be known as Corpus Iuris Civilis, but at the time it lacked diffusion and was known through compendiums that deformed it. The renaissance in Roman studies during the 12th and 13th centuries that would influence all of Europe, occurred in Bologna, a city in the Italian Romagna. It wasn't small, in this diffusion, the role of the romano-Germanic emperors, who were moved by their political interests as much as by their supposed condition of successors to the old Roman Empire. The teachers of this most famous "school of Bologna" acted according to a method of medieval study, the one of glosses or commentary of the content and meaning of justinian texts. They are not critical commentaries, but rather, analytical. The bolognian professors accept justinian law as something superior, even supreme; they are limited to comment on it, without too much critical baggage, because for that they needed philological command of Greek language and study of original texts and historical knowledge, in which they were lacking. But from their commentary fundamental consequences for the Europe of the time are deduced, by the creation of a rich casuistry that covered a field of superior and more ample legal hypothesis from what was widely known until then. The foundation of this school of bolognian professors is due to Irnerius at the beginning of the 12th century. Disciples of his were Hugo de Porta Ravennate, Bulgarus, Jacobus de Boragine and Martinus Gosia, called "the four doctors" because of their wisdom and influences. All of them were Ghibellines (supported the idea of the Empire being over the pontificate) and in favor of Frederick I, of whom they were contemporary.

Around the same time, with some decades of difference, a systematization of the ecclesiastical law took place, which was going to give birth to the canon law in all its fullness. Romanists and canon lawyers were brothers of mentality and duties, although the later defended the pontifical rights. The first one to compile and systematize the previous universal council canons was Graciano, a theology teacher from bologna, who wrote ca. 1140 his Concordance of the Discordances of the Canons, commonly called Decree. The work of Graciano did not have official status, but it reached great prestige and caused in the following decades a height in legal consultations formulated to the pontiff s, something to be expected at a time of insufficient organization of the civil power. These answered by means of litteras decretals or "decretals", whose compilation became necessary, as the only way to use and preserve the judiciary wealth they had, since they not only affected ecclesiastical matters, but also those of civilians and secular people.