Confoederatio cum principibus ecclesiasticis

The Confoederatio cum principibus ecclesiasticis ("Treaty with the princes of the church") was decreed on 26 April 1220 by Frederick II as a concession to the German bishops in return for their co-operation in the election of his son Henry as King. It was an important source of law of the Holy Roman Empire, and was counted among its constitutional documents by the editors of the Monumenta Germaniae Historica.

Source: Wikipedia — Confoederatio cum principibus ecclesiasticis (CC BY-SA 4.0)