Pontificale Romano-Germanicum

The Pontificale Romano-Germanicum (Roman-Germanic pontifical), also known as the PRG, is a set of Latin documents of Catholic liturgical practice compiled in Saint Alban's Abbey, Mainz, under the reign of William (archbishop of Mainz), in the 10th century and an influential work in the establishment of the Catholic Church in Europe. It was in wide circulation during the Middle Ages and was used as the basis for the modern Roman Pontifical.

Source: Wikipedia — Pontificale Romano-Germanicum (CC BY-SA 4.0)