We owe the preservation of many of these consular and mythological diptychs to the circumstance that when the practice of sending them as presents had (it may be) for some time been discontinued, another use was found by adapting them to Christian purposes. In some cases the subjects or titles of the diptychs were altered; as, for example, in one of the diptychs preserved at Monza. This was originally a consular diptych, of late work, coarse in style and manner of execution. The consul is represented on each wing, raising the _mappa circensis_ in the usual way: on one, however, he is standing; on the other he is sitting upon a kind of throne. On one leaf the top of the consul’s head has been shaved, to show the clerical tonsure; and in the blank space of two small panels, immediately beneath the arch under which he stands, the title S[an]C[tu]S GREG^oR[ius] is cut in high relief. On the other leaf above the sitting consul, on the corresponding panels, DAVID REX is inscribed in similar letters. Both the wings are engraved by Gori. It must not be omitted that some late writers have argued that this diptych is not a palimpsest; that it is merely an imitation of the preceding consular diptychs, and not earlier than the seventh or eighth century. But the whole character is unlike mere imitation; and the shaving of the head, the alteration of the ornamented top of the sceptre or staff, and the cutting of the inscription on the tablets, might without difficulty have been made for the required and more modern purpose. It is easy to understand how later possessors of consular diptychs were induced to make presents of them to their bishops and churches; and in some instances, probably, in the sixth century, those originally sent to high ecclesiastical persons were at once transferred to pious uses. Instead of containing the lists of the consuls, the diptychs then inclosed the names of martyrs, saints, or bishops who were to be commemorated in the public service of the Church. These lists were read at mass: of the saints at that part of the canon which is now known as the _Communicantes_; and of the dead at the _Memento_, after the consecration of the Eucharist. Frequent reference to the custom is to be found in the old ritualists, and full information and a cloud of authorities on the subject in the learned work of Salig, on diptychs. The leaves of several such diptychs still exist, and sometimes with the names not written on wax, but carved or incised upon the ivory itself. One very remarkable example is the diptych, now at Liverpool, of Flavius Clementinus, consul A.D. 513. Upon the back of each leaf a long Greek inscription has been incised, done, beyond doubt, in the first year of pope Hadrian, A.D. 772, when the diptych was given to some church for sacred use. The list of names inscribed, to be prayed for, includes that of the donor.