The Christian diptychs were intended for four purposes. First come those in which the names of all the baptised were entered, a kind of _Fasti ecclesiæ_, and answering to the registers kept now in every parish. Second, those in which were recorded the names of bishops and of all who had made offerings to the church or other benefactions. This list included the names of many persons still living. Third, those in which were recorded the names of saints and martyrs; and, naturally, in various places the names would be particularly of saints who in their lives had been connected with the locality. Such additions are of the utmost importance in tracing the history of ancient lists which have come down to our own time. Diptychs of this class were read aloud at mass, as a sign of the communion between the Church triumphant and the Church militant on earth. Fourth, those in which were written the names of dead members of the particular church or district, who having died in the true faith and with the rites of the church were to be remembered at mass. As regards the living, the continuance of their names in the diptychs was of the highest consequence; to be erased was equal to the denunciation of them as heretics and unworthy of communion. In the diptychs also were probably sometimes added the names of people who were sick or in trouble. But besides these four objects for which Christian diptychs were made, there was another which must certainly have caused the production of many large sculptured works in ivory from the seventh to the tenth century: namely, for the purpose of exciting devotion and as a means also of teaching the ignorant. Ivory tablets or diptychs of this description are ordered to be exposed to the people in the old Ambrosian rite for the church of Milan.