This painting was part of the predella (the bottom tier) of the Maestà altarpiece made for the Cathedral of Siena.
Virtual reconstruction of the Maestà Altarpiece (1308-1311).
Virtual reconstruction of the Maestà Altarpiece (back).
Reconstruction of the reverse of the Maestà altarpiece showing the probable location of the Kimbell panel at the bottom right of the predella. After John White, published in Giotto to Durer: Early Rensaissance Painting in The National Gallery by Jill Dunkerton et al., 1991.