Ages, were usually of a devotional character, although sometimes
secular subjects occur. Letters were sometimes written on ivory
tablets, which were supposed to be again used in forwarding a reply.
St. Augustine apologizes for writing on parchment, explaining, "My
ivory tablets I sent with letters to your uncle; if you have any
of my tablets, please send them in case of similar emergencies."
Tablets fitted with wax linings were used also in schools, as children
now use slates.

Ivory diptychs were fashionable gifts and keepsakes in the later
Roman imperial days. They took the place which had been occupied
in earlier days by illuminated books, such as were produced by
Lala of Cyzicus, of whom mention will be made in connection with
book illuminators.

[Illustration: THE NATIVITY; IVORY CARVING]

After the triptychs came sets of five leaves, hinged together;
sometimes these were arranged in groups of four around a central
plaque. Often they were intended to be used as book covers.
Occasionally the five leaves were made up of classical ivories
which had been altered in such a way that they now had Christian
significance. The beautiful diptych in the Bargello, representing
Adam in the Earthly Paradise, may easily have been originally
intended for Orpheus, especially since Eve is absent! The treatment
is rather classical, and was probably adapted to its later name.
Some diptychs which were used afterwards for ecclesiastical
purposes, show signs of having had the Consular inscription erased,
and the wax removed, while Christian sentiments were written or
incised within the book itself. Parts of the service were also