Vatican Museum
The Florentine painter Giotto di Bondone completed this richly gilded double-sided work between 1320 and 1330. It had long been thought to have been made for the main altar of the church; more recent research suggests that it was placed on the "canon's altar", located in the nave, just to the left of the huge arched opening into the transept. The altar was freestanding, and the altarpiece is painted on both sides so it could be seen by the congregation from the front and the canons of the church from the back.
Raphael circa 1518-1520 Vatican Museum.