Altarpiece two, three, and multiple panels respectively. In the thirteenth century each panel was usually surmounted with a pinnacle, but during the Renaissance, single panel, or "pala", altarpieces became the norm. In both cases the supporting plinth, or "predella" often featured supplementary and related paintings. 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. A single church can furthermore house several altarpieces on side-altars in chapels. Sometimes the altarpiece is set on the altar
St John Altarpiece (Memling) it presents a narrative, meant to emulate a vision the donors or viewers would experience when viewing the inside panels. Unlike most altarpieces of these types, Memling's fails to present a single unifying iconographical focus and is quite generalized with themes that seem unsuited for its specific location, according to Blum. She speculates the donors may have chosen the specific iconography, which "celebrated intercessory saints on the interior". It is an unusual painting in that it seems to "have served a double function: that of personal propitiation and that of public altarpiece, which portrayed the role of the religious community