The triumphal entry of Christ into Jerusalem.Detail of the "Five-Part Diptych" (so named because each panel is divided into five plates), a beautifully carved Gospel book cover dating from the late 5th or early 6th century and probably made in Ravenna. It is now kept in the Milan Cathedral Treasury. There are notable similarities in the iconography with 5th-century sarcophagi and early 6th-century mosaics of Christ in Sant'Apollinare Nuovo. It may have been a gift from the Byzantine emperor. By the 12th century it was no longer used as a book cover, but in the Vespers liturgy of Easter processions. After 1400 it was used as part of a "Pax," a metal plate with a handle presented during the kiss of peace ritual.