Imperial diptych offerings to the emperor. However, the fact that the Barberini ivory was almost certainly not a diptych, but some kind of imperial icon without a second panel is a serious argument against the existence of the imperial diptych type. The two panels representing the empress Ariadne, in the Bargello in Florence and the Kunsthistorisches Museum in Vienna, also belong to the hypothesied imperial diptych type. They are the only central panels of such a diptych (other than the Barberini ivory) to survive, since all other fragments of such diptychs are from side panels. Imperial diptych In Late Antiquity, an imperial
Saint Peter Martyr Altarpiece testimony) also mention a second altarpiece by the artist in the same church, also dating to 1476, now known as the "Saint Peter Martyr Altarpiece"'. It is therefore theorised that the altarpieces were both dismantled during rebuilding of the church in 1776, then sold to the antiquarian Grossi who sold all the panels separately and grouped some of them into the altarpiece that Cardinal Zelada bought from him. Federico Zeri and Rodolfo Pallucchini then joined the altarpieces together, initially referring to the first (the high altarpiece), the "Pietà" in the Metropolitan Museum, and then to the "Madonna" in the Museum