What is the function of the category utilitas publica in the writings of the classical jurists? It serves to legitimate leges publicae, as in the case of Augustus' lex Iulia et Papia. Secondly, utilitas publica is cited as the rationale of a given lex publica for the purpose of its interpretation, and in the third instance it is a guideline for the creation of new law by the jurists themselves. The part of Roman law, which is derived from utilitas publica, is called ius publicum. In this sense it has an assortative function. Due to its origin in natural law thinking and its public nature utilitas publica is the creative principle behind the first norms aiming at the protection of the environment.