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.[3]