Large number of altarpieces are now removed from their church settings, and often their elaborate sculpted frameworks, and displayed as more simply framed paintings in museums and other places.
Altarpieces seem to have begun to be used during the 11th century, with the possible exception of a few earlier examples. The reasons and forces that led to the development of altarpieces are not generally agreed upon. The habit of placing decorated reliquaries of saints on or behind the altar, as well as the tradition of decorating the front of the altar with sculptures or textiles, preceded the first altarpieces.
Many early altarpieces were relatively simple compositions in the form of a rectangular panel decorated with series of saints in rows, with a central more pronounced figure such as a depiction of Mary or Christ. An elaborate example of such an early altarpiece is the Pala d'Oro in Venice. The appearance and development of these first altarpieces marked an important turning point both in the history of Christian art and Christian religious practice. As pointed out in the Grove Encyclopedia of Medieval Art and Architecture, "The advent of the altarpiece marks a significant development not only in the history of the altar, but also in the nature and function of the Christian image. The autonomous image now assumed a legitimate position at the centre of Christian worship."
Painted panel altars emerged in Italy during the 13th century. In the 13th century, it is not uncommon to find frescoed or mural altarpieces in Italy: mural paintings behind the altar function as visual complements for the liturgy. These altarpieces were influenced by Byzantine art, notably icons, which reached Western Europe in greater numbers following the conquest of Constantinople in 1204. During this time, altarpieces occasionally began to be decorated with an outer, sculptured or gabled structure with the purpose of providing a frame for individual parts of the altarpiece. Vigoroso da Siena's altarpiece from 1291 (pictured) display such an altarpiece. This treatment of the altarpiece would eventually pave the way for the emergence, in the 14th century, of the polyptych.
The sculpted elements in the emerging polyptychs often took inspiration from contemporary Gothic architecture. In Italy, they were still typically executed in wood and painted, while in northern Europe altarpieces were often made of stone.