Generally, a diptych is two panels of equal size joined together by some device, usually a hinge. The form follows a long tradition that began in late Western antiquity, when Romans appointed to the consulate in the 4th – 6th centuries A.D. commissioned ivory tablets carved with their own likenesses on each panel (before we criticize smartphone selfies as a symptom of contemporary narcissism, we might look first to our uncanny doppelgangers, the Ancient Romans). The tablets were connected by a hinge, and closed like a book to protect the inside—a thin layer of cool wax where the consul could write with a stylus and, if necessary, erase. The diptych was, essentially, a ceremonial notebook used to track and record consular appointments by year. When, in the next few centuries, the consular diptychs were reused by the early Christians, the insides of the tablets were erased and used to record prayers for the living church community in Western Europe. In Eastern Europe, they were used to record prayers for the dead. Elsewhere, the ivory tablets were used to keep track of the growing list of saints and their appointments by year. (The early history of the diptych, then, is history itself.)
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