Earthenware pots or vases were sometimes embedded in structures to improve the acoustics. Celebrated examples are the dome of San Vitale (c. 540–48), and the Orthodox Baptistery (c. 400–50), both in Ravenna, but in both cases the base of each vase fits into the mouth of the vase below, forming structural ribs or tubes, the spaces between being filled with concrete. Earthenware pots are found embedded in the walls of many medieval churches, e.g. in the South of France, in Normandy, in Cologne, and in The Netherlands. Also called dome-pot, pottery vaulting.