In the beginning there was peace: At the close of the tenth century and the commencement of the eleventh, thepax Dei,the Peace of God—a peace movement carried out in the name of God—emerged in the territories that today make up central France. Thepax Deiin turn led to the establishment of thetreuga Dei—the Truce of God. Yet these peacemaking efforts together resulted in the crusade at the end of the eleventh century. A new kind of holy war grew out of the holy peace.¹

Peace is a central issue of power, and the...

In the aftermath of the First Crusade, Guibert of Nogent wrote: “In our own time God has instituted a holy manner of warfare [instituit nostro tempore praelia sancta Deus], so that knights [ordo equestris] and the common people who, after the ancient manner of paganism, were formerly immersed in internecine slaughter, have found a new way of winning salvation. They no longer need, as formerly they did, entirely to abandon the world by entering a monastery or by some other similar commitment. They can obtain God’s grace in their accustomed manner and dress, and by their ordinary way of life.”¹...

Christendom,christianitas,was the form of Western unity that emerged in the High Middle Ages. Medieval writers spoke of Christendom when they talked about themselves and their civilization.¹ People described themselves as inhabitants of Christendom when they wished to refer to the “limits of a society larger than their village or parish, county or diocese, or kingdom.”²Christendomwas the most common term for the lands inhabited by Latin Christians, designating “a community of powers and nations united by their shared religion,” or simply, “Christian society.”³ Medieval thinkers invested the idea of Christendom with their hopes for temporal as well...

In chapter 3, I examined the role that the crusade idea and crusading movement played in the articulation of structures of public authority and the formation of political order in the Latin West. To round out the picture of those developments, I now turn to some leading intellectual and spiritual figures of the twelfth and thirteenth centuries and the ways they thought about the relation of Christendom to the Muslims. I show how these different ideas blended into an overall hostile view of the non-Christian world. With regard to the Muslim world, this hostile outlook was organized along two main...

The papal monarchy sank with its banners flying high. Pope Boniface VIII’s opening words in his famous bull of 1302, theUnam sanctam,do not lack confidence: “That there is one holy, Catholic and apostolic church we are bound to believe and to hold, our faith urging us, and this we do firmly believe and simply confess; and that outside this church there is no salvation or remission of sins.” The bull was a clear statement of papal monarchism. Firstly, the one and unitary church was monarchical in structure: “there is one body and one head of this one and...

The decline of Christendom involved the weakening of the two competing forms of medieval universal power—the papal monarchy and the empire. At the same time, the ascending territorial kingdoms attempted to appropriate Christendom’s universalism. During this long and uneven process both defense and questioning of the idea of universal rule played a part. In this chapter, I first discuss the work of three late medieval writers who defended the empire as the legitimate world monarchy, necessary for the establishment and maintenance of universal peace and the defense and spread of Christianity. I then present the ideas of three of...