A painting (more rarely a sculpture) placed on, behind, or above an altar in a Christian church. Altarpieces vary greatly in size, construction, and number of images ( diptych , triptych , and polyptych ). Some are small and portable; some (known as a retable or reredos – there is no clear distinction) are fixed. A typical Italian altarpiece has a large central panel, flanked by subsidiary panels, with a predella , or strip of scenes, across the bottom. Spanish altarpieces tend to be architecturally elaborate retables. A popular form in northern Europe was the winged altarpiece , in which outer wings are hinged so that they can be closed to cover the centre panel; the backs of the panels are usually painted in a less elaborate fashion. Outstanding altarpieces include Duccio's Maestà (1308–11, Cathedral Museum, Siena), Mathias Grünewald's Isenheim Altarpiece ( c. 1515, Unterlinden Museum, Colmar), and Jan van Eyck's Adoration of the Lamb (1432, St Bavon, Ghent). Few altarpieces survived…