After statues of Dacian captives originally in the Forum of Trajan which were by 1540-42 in the Palazzo Farnese. Another sheet of studies after the antique by Franco in the Louvre (inv. no. 4968) depicts both statues and the Hercules Farnese, P. Bober and R. Rubinstein, Renaissance Artists and Antique Sculpture, A Handbook of Sources, London, 1986, p.198, under no. 165 a-b.