An altarpiece is a picture or relief representing a religious subject and suspended in a frame behind the altar of a church. The altarpiece is often made up of two or more separate panels created using a technique known as panel painting. It is then called a diptych, triptych or polyptych for two, three, and multiple panels respectively. In the thirteenth century each panel was usually surmounted with a pinnacle, but in the Renaissance, single panel, or pala, altarpieces became the norm. In both cases the supporting plinth, or predella often featured supplementary and related paintings. In the eighteenth century altarpieces, such as Piero della Francesca's polyptych of St Augustine, were often disassembled and seen as independent artworks.
If the altar stands free in the choir, both sides of the altarpiece can be covered with painting. The screen, retable or reredos are commonly decorated.
Groups of statuary can also be placed on an altar. Sometimes the altarpiece is set on the altar itself and sometimes in front. Originally, the altarpiece was placed in front of the altar, with the priest standing behind it facing the congregation. In the 13th century, the altarpiece moved behind the altar, with the sacrament placed in front of it and the priest standing with his back to the congregation. This placement to behind the altar allowed the altarpiece to expand to larger proportions, as during the Renaissance.
Famous examples include: