The Council of Mopsueste, in 550, ordered the churches to keep the diptychs, and the names of those persons to be prayed for during the celebration of mass to be inscribed in them, in the following categories, all having a more or less local connection with the particular church:
Firstly: Neophytes, or newly baptized;
Secondly: Benefactors, Sovereigns and Bishops;
Thirdly: Saints and Martyrs; and
Lastly: The Faithful Dead “in the sleep of peace.”
People were very anxious to have their names inscribed, and fearful of being scratched out for heresy.
For the dead bishops the prayer was less for them, than to them, from which comes the word “canonize,” or to be named in the Canon of the Mass. On the inner side of the diptych of Clementinus, at Liverpool, there is in roughly written Greek letters a prayer for the clergy of a church of St. Agatha, and for “our Shepherd Hadrian the Patriarch,” who can be none other than Pope Hadrian (✝795); this diptych probably came from a church in Sicily, for Greek was still spoken, and the patron saint of Palermo is St. Agatha.
Lists of bishops were inscribed, and when the list grew too long parchment leaves were inserted. Whole services were bound in these carvings, and the covers of many of the oldest MSS. are of diptychs, set in an elaborate border of goldsmith’s work, to increase the size as well as to enhance the beauty.