A study for the Chigi chapel frescoes in Santa Maria della Pace, Rome

A photograph of a drawing now in the National Gallery, Stockholm (inv.no. 325/1863) attributed to the circle of Raphael and considered to be an early idea for the frescoes The four prophets and The four sibyls painted by the workshop of Raphael c.1511-14 in the Chigi Chapel in Santa Maria della Pace, Rome. Annotated on verso.

This drawing was previously attributed to Timoteo Viti. An earlier sketch for this composition is on the verso of a drawing by Raphael for the School of Athens in the Ashmolean Museum, Oxford (inv.no.WA1846.194; see RCIN 852564 for a photograph of the recto of this drawing).
 
Raphael was commissioned, probably early in 1511, by the banker Agostino Chigi to decorate his chapel in Santa Maria della Pace. The initial plan of decoration for the chapel included frescoes, two bronze roundels and an altarpiece; however, whilst Raphael executed some designs for the altarpiece, which was to depict the resurrection, it was never executed, and the bronze roundels, whilst cast, appear to never have been installed. The frescoes comprise two registers, with four prophets on the top  (flanking a window) and four sybils below. According to Vasari, portions of the frescoes were painted by Timoteo Viti.