This book has two main aims. The 􀀀rst is to provide atightly focused account of the most pivotal episodein the historical evolution of the idea ofsovereignty—which I de􀀀ne generically as thesupreme authority to command, legislate, andjudge—in the thirteenth century. Although theexisting historiographical literature is repletewith studies that trace the evolution of thatidea—even if they don't use the word “sovereignty”to describe it—in the fourteenth, 􀀀fteenth, andsixteenth centuries, no such account exists for thethirteenth century. To be certain, over the pasthalf-century or so a great deal of research has beendone on aspects of the political thought during thisera. But these e􀀀orts have tended to be fragmented,following di􀀀erent lines of inquiry, andemphasizing di􀀀erent themes. A conceptually focusedinterpretation, one foregrounding the role played bythirteenth century thought in the evolution of acoherent theory of sovereignty, has been lacking. Myhope here is to begin to address this lacuna byproviding an account of how a series ofthirteenth-century contests over the locus andcharacter of supreme authority ultimately made itpossible “to imagine that we inhabit a world of[sovereign] states.”

My secondary goal, hinted at in the epigraphs above, isto reconnect early modern theorists of sovereigntyto the medieval intellectual tradition out of whichthey emerged. Thinkers like Bodin and Vattel did notinvent the modern concept of sovereignty out ofwhole cloth. r ather, they assembled it out of theintellectual resources inherited from their medievalforebears, in the 􀀀rst instance fromfourteenth-century thinkers like Marsilius, Baldus,and Bartolus, but via them from thethirteenth-century thinkers discussed in thisbook.