Screen of stone or wood at the back of the altar, usually ornamented with panels, niches, statues, buttresses, and other decorations and often painted in brilliant colors. The side which faces the nave is called the “retable” and the other side, the “counter-retable.” It sometimes extends across the whole breadth of the church and reaches nearly to the ceiling. Its use dates front the 12th century, when only the altar of relics had a reredos, but in the 14th century the main altar was provided with one and it became an elaborate structure, usually conforming to the architecture of the church. It is connected with the altar by means of a predella or altar step. In medieval times it was customary in some places to keep the Blessed Sacrament in a small cupboard arranged in the reredos.