Related to the reverse of a medal issued by Pope Innocent X on the feast day of Saints Peter and Paul on 29 June 1651, J. Montagu, Alessandro Algardi, New Haven and London, 1985, pp. 92-3, illustrated. The medal, minted by Gaspare Morone of the Papal mints, has on the obverse a portrait of Pope Innocent X. The legend around God the Father reads 'FIAT PAX IN VIRTUTE TUA.'.
Dr. Jennifer Montagu proposed that the designs for the medals of 1650 and 1651 were based on Algardi's designs, and connected the one of 1651 to the marble of God the Father with two putti over the altarpiece of Saint Nicholas of Tolentino in the church of that name in Rome. Algardi probably based the present drawing on that sculpture, adapting it to the circular format.
Algardi had close connections with the Papal mint as the die engraver Morone was one of his closest associates and the president, Giacomo Franzone, was Algardi's patron.