Descriptions, examples, and links
Predella: A subsidiary picture forming an appendage to a larger one, especially a small painting or series or paintings beneath an altarpiece.
Altarpieces divide into two main types: the reredos, which rises from ground level behind the altar, and the retable, which stands either on the back of the altar itself or on a pedestal behind it. Many altars have both.
Source: © 14 Oct 2002, Nicolas Pioch - Top - Up - Info
Defining the Altarpiece
There are many kinds of altarpieces, and you have been given examples in previous weeks. The basic definition of an altarpiece is that it is a picture of some sacred subject painted on the wall or suspended in a frame behind the altar, or a group of statuary on the altar. Altarpieces have evolved over the century, but in the Middle Ages, instead of a picture or group, the altarpiece consisted in some churches of embossed silver or gold and enamelled work set with jewels. Sometimes the piece was set on the altar itself. Sometimes a folding door was attached which covered the picture during the year, and was opened on grand festivals to expose the picture. If it was a movable structure, it was made of hammered silver or other precious material, supported on the altar itself. The face of this structure which looks towards the nave of the church is called the "retable", and the reverse is called the "counter-retable". This decoration of the altar was not known before the twelfth century. It should always correspond to the architecture or style of the church. The best models are found in the churches of St. Sylvester in Capite, Sta. Maria del Popolo, della Pace and sopra Minerva, at Rome. When this structure is ornamented with panels and enriched with niches statues, buttresses, and other decorations, which are often painted with brilliant colours, it is called a "reredos". Sometimes the reredos extends across the whole breadth of the church, and is carried nearly up to the ceiling. This decorative screen, retable, or reredos is also called the altarpiece.
Different kinds of altarpieces.
Madonna with the Child, Saints and Crucifixion - Fra Angelico