 A distinction among kinds of laws, namely natural law (ius naturale), law of nations (ius gentium), and civil law (i.e., the law of a particular community). The law textbooks were perhaps the main source of the idea of natural law, so important to later medieval political thought. This idea can be traced back to Cicero, to the Stoics, and to Aristotle, but most medieval political philosophers encountered it in Gratian’s Decretum. (As a rule, medieval theologians and philosophers evince a greater familiarity with the collections of canon law than with the Corpus iuris civilis.)