Ptolemy, considered a proto-Humanist by some, combined the principles of Northern Italian republicanism with Aristotelian theory in his "De Regimine Principum," a book that influenced much of the political thought of the later Middle Ages, the Renaissance, and the early modern period. He was the first to attack kingship as despotism and to draw parallels between ancient Greek models of mixed constitution and the Roman Republic, biblical rule, the Church, and medieval government.

In addition to his translation of this important and radical medieval political treatise, written around 1300,...