MEDIEVALISTS WHO TAKE an interest in the history of power tend to come across the words potestas or auctoritas in historical documents, more rarely the term imperium; they are generally translated by “power,” “authority,” or “empire.” The first two are used as synonyms when defining “dominion, empire, faculty, and jurisdiction that one has to command or execute something”, in other words the capacity of a king to govern a country, while the latter term refers to a power with universal tendencies. However, the fact that in Spain, some kings of Leon and then Castile bore the title of imperator has generated various theories, in many cases controversial, over the last century, and even the idea that the appropriation of such a title responded to the needs of a weak monarchy, with little “power,” that required and thus obtained an “increase in legitimacy.”

The vast majority of medievalists who have dealt with this problem did so comparing the Hispanic case with contemporary cases or ones not very distant in time. Whoever says “empire” then evokes either the Carolingian empire of the ninth century or the Holy Roman Empire of the eleventh to thirteenth centuries. The comparisons are always established within the traditional “medieval” framework—the years 500 to 1500—, “horizontally” and not “vertically” over time. The division between Antiquity, Middle Ages, and Modern Times often plays the role of an insurmountable frontier: as if each of these epochs invented everything without inheriting anything from the previous age or transmitting anything to the subsequent period. In 1977, Régine Pernoud published a short book with a provocative title: Pour en finir avec le Moyen Âge, a work that she began by recalling a question she had been asked: “Could you tell me the exact date of the treaty that officially ended the Middle Ages?” The sentence brought a smile to the face of more than a few medievalists who read it from the heights of their discipline and their wisdom. They should not have smiled, because most works dedicated to the Middle Ages display the firm conviction that, one fine day, Antiquity ended and disappeared, remaining as a distant memory, and that the Middle Ages began then, sufficient unto itself; in the same way, the Modern Age will not have any point in common with the centuries that preceded it.