This is a “closure slab,” which would have been placed in a Byzantine church at the base of the screen separating the laity from the priesthood. A lion eats fruit from a tree of life, symbolizing salvation; the arch bears an inscription in pseudo-Kufic, the earliest form of Arabic calligraphy.
Closure Slab with a Lion and Pseudo-Kufic Inscription, about A.D. 1000, made in Corinth, Greece. Marble, 35 1/16 in. high. Image courtesy of the 25th EBA, inv. no AM391
In Heaven and Earth: Art of Byzantium from Greek Collections