Canon law:

The Catholic Church has what is claimed to be the oldest continuously functioning internal legal system in Western Europe, much later than Roman law but predating the evolution of modern European civil law traditions. What began with rules ("canons") adopted by the Apostles at the Council of Jerusalem in the first century has developed into a highly complex legal system encapsulating not just norms of the New Testament, but some elements of the Hebrew (Old Testament), Roman, Visigothic, Saxon, and Celtic legal traditions.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". What does the Catholic Church claim to be the oldest of in the world?
unanswerable