Hugo Grotius was a major figure in the fields of philosophy, political theory and law during the sixteenth and seventeenth century. Along with the earlier works of Francisco de Vitoria and Alberico Gentili, he laid the foundations for international law, based on natural law in its Protestant side. Two of his books have had a lasting impact in the field of international law: "De jure belli ac pacis" ["On the Law of War and Peace"] dedicated to Louis XIII of France and the "Mare Liberum" ["The Free Seas"]. Grotius has also contributed significantly to the evolution of the notion of "rights". Before him, rights were above all perceived as attached to objects; after him, they are seen as belonging to persons, as the expression of an ability to act or as a means of realizing something.