Concordats

A treaty between the Holy See and a state, which makes it an instrument of international law and of canon law at once. What a concordat settles is usually the same short list: who appoints bishops, what the church owns, what it may teach and whether the state pays for any of it. They are signed at moments when both parties want something, and the terms record what each was prepared to trade, which is why they read very differently a century later than they did on the day.