The signed portrait depicts the Earl of Charlemonte (1728-1799) as an architect clad in an antiquizing tunic holding a measuring scale in one hand and a ground plan sketch of a building in the other. The lord is leaning against a commemorative slab dedicated to Vitruvius. Placed on a high pedestal behind Charlemonte’s back is a bust of Andrea Palladio. The allegorical figure of Architecture is explaining to the draughtman that the study of Vitruvius is no longer purposefull and that instead he ought to turn his attention to modern architecture represented by Palladio. The painting was produced after the Earl’s return from his Grand Tour during Mengs’s professional career in Rome. Behind the execution of this painting are most likely the events associated with Piranesi’s volume entitled Antichita Romae, for the publication of which he had counted on Charlemont’s financial support that the Earl promised him in the past but which he later no longer acknowledged. Piranesi was outraged by the lord's behaviour, however Charlemont lost interest in Piranesi's work, due to the development of his opinion regarding architecture and to his own practice in the Neo-Classical style. In 1757, he wrote his Lettere di Giustificazione scritte a Milord Charlemont that he distributed among his Roman and British friends. Mengs also received one copy. The portrait of the Earl of Charlemont had probably been finished by then.