Cf. G. M. A. Richter, Engraved Gems of the Romans, London, 1971, no. 545; M. Henig, The Lewis Collection of Gemstones, Oxford, 1975, no. 15; and S. H. Middleton, Engraved Gems from Dalmatia, Oxford, 1991, p. 113, no. 202, for intaglios of the philhellenic emperor Hadrian. Also see, S. De Caro, The National Archaeological Museum of Naples, Naples, 1996, p. 348, inv. 26088, for an amethyst intaglio of Antoninus Pius "in the attitude of a Greek philiosopher. The soft and very fine rendering of the beard and hair is typical of the pictorial style of the period".