Catechism of the Catholic Church §1979 — excerpt
The natural law is immutable, permanent throughout history. the rules that express it remain substantially valid. It is a necessary foundation for the erection of moral rules and civil law.
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.