Large and detailed micromosaics depicting St. Peter's Square with the domed Basilica and Vatican beyond were ever popular with tourists, and the vista was favored by mosaicists during the 19th century. However, it is unusual to find an example of such proportion and detail as the present lot. Pope Pius IX is visible on the balcony of the Basilica giving the Papal Blessing to the throng of people in the piazza below. Among the numerous people and carriages, standout details include mounted cavalry officers, women in elaborately-knitted shawls and viewers in an open carriage, owning to the immense skill of the mosaicist Biagio Barzotti.
For large scale mosaics, the workshop originally used cubic tesserae, known as smalti, made from ground glass and baked in an oven like enamel. By the 1760s this art had been so perfected that it was possible to produce rods or threads of colored glass, called smalti filati, thin enough to be cut into the minute tesserae used on the present lot. These tiny individual tesserae in an almost limitless palette of as many as 28,000 colors allowed truly painterly compositions, such as the subtle rendering of the fountains spraying in the wind. By the 19th century, the Vatican workshop, for whom Barzotti eventually worked, was producing such superior mosaic-work that it operated at the near exclusion of any other mosaic studio.