This is from Stephen Grabill's introduction to Zanchi's "On the Law in General":
Before concluding, it should be mentioned that Zanchi’s understanding of the types of law was particularly influential upon the Reformed political theorist and city attorney of Emden, Johannes Althusius (1557-1638). According to Frederick Carney, the translator of Althusius’s Politica, it was Zanchi’s extensive discussion of law that more than anything else contributed to “Althusius’ understanding of the relation of the Decalogue to natural law, and of both to the proper laws of various nations.” Althusius thought that magistrates should administer a commonwealth on the basis of prudence, which involves knowledge both of law and of the changing and contingent circumstances to which law is to be applied. “The discussion of law at this point,” observes Carney, “is an extended treatment of the relation of the Decalogue to natural law, and of the role of these two together as common law in the formulation of proper law for particular societies.” Zanchi’s positive assessment and affirmation of natural law in his so-called Treatise on Law bore much fruit in the life and work of Althusius, who, in Carney’s judgment, “maintained a rather warm appreciation for a human’s natural knowledge of one’s duty to both God and neighbor.”
In the literature of political philosophy Althusius is treated variously as a proto-liberal prophet of the social contract, a precursor to modern federalism (though not of constitutional federalism, as Thomas Hueglin points out), or a pre-Kuyperian. The above passage, once more, is from the new issue of the Acton Institute's journal, Markets & Morality, admittedly a somewhat off-putting title. (Why not just call it the Acton Journal?)
Here is more on the life of Hieronymus (or Girolamo) Zanchi: "The Life of Zanchi." His connection with Frederick III, "the Pious," who commissioned the Heidelberg Catechism, is particularly interesting.