Executed on the same scale as the print, the drawing offers fascinating evidence for Desprez’s working-method. To achieve the complex perspective of the architecture, Desprez was required to insert several strips of paper to correct earlier errors, before adding elaborate architectural elements with a fluid pen line, radically abbreviating certain details. These details, in turn, were refined and focused by Piranesi in the finished etching, the prints appeal to travellers being, in part, their architectural and topographical accuracy. The result in the present watercolour is a grand tonal essay, which is less about ornamental verisimilitude and more about capturing the romantic appeal of the crepuscular, candle-lit basilica. The drawing, made on a thick piece of Dutch, laid paper with the watermark for J Honig & Zoonen, is worked on both sides. The verso shows a complex study of Mezentius Fatally Wounded by Aeneas, a design Desprez would work up further in a serious of more finished studies. As such, this process sheet, offers unparalleled insight into Desprez’s method and his relationship with Piranesi.