Michael Wilks’s best-known contribution to historical scholarship is The Problem of Sovereignty in the Later Middle Ages (Cambridge, 1963). This is an exploration of the political ideas of Augustinus Triumphus of Ancona (c. 1270-1328) and his contemporary publicists on the nature of sovereignty—or supreme authority—and its location within society. Like most medieval thinkers Augustinus saw society as the universal Church, the body of Christ, a single corporate entity which embraced all Christians, and within which all were united in pursuit of the common aim of salvation. Most thinkers would have agreed, too, that in theory society itself was the possessor of sovereignty. The ‘problem’ arose in trying to decide how and by whom sovereignty should be wielded in practice. There were various solutions. At one extreme the pope, as the vicar of Christ, was thought to represent Christ’s mystical body, the Church, on earth. He thus became the physical embodiment of sovereignty, and, as such, the sole source of power within society.