An oil sketch by Giovanni Battista Gaulli, known as Baciccia, depicting the Holy Trinity, was placed underneath Raphael’s statuesque depiction of St. Peter in a trompe l’œil niche. According to the inventory of 1800 “Sotto al medesimo un Bozzetto rappresentante la SS. Trinità del Baciccio.” In the inventory of 1791 this painting may be recognized as “bozzetto di Bacicio p3 — Padre Eterno.” The painting is assigned the size of 3 palmi, implying a surface area of 9 palmi.

The bozzetto is probably to be identified with an oil sketch entitled “Trinità in gloria” and measuring 50 x 98 cm at the Galleria nazionale dell’arte antica in Rome (Palazzo Barberini), inv. 2567; cf. Dipinti dei Musei e Gallerie di Roma (Rome, 1998), vol. IV, p. 96. The width corresponds to more than 4 palmi while the height is less than 2 palmi. Since the dimensions in this inventory are given principally in order to itemize the costs of cleaning and varnishing of the individual paintings, the main concern was the total surface area.

The bozzetto, which must have been executed shortly after 1670, soon joined the collection Cardinal Camillo Massimi (1620-1677), the pope’s chamberlain, at the Palazzo alle Quattro Fontane. It is listed as item 104 in the Cardinal’s posthumous inventory, drawn up on 11 October 1677, about a month after his death. The painting, which passed to his brother Marchese Fabio Camillo Massimo (1621-1686), is described as: “Un Quadro bislungo longo p.mi 4. in circa alto p.mi 2. in circa rappresenta la Ssm.a Trinità di mano del Baciccio”. The inventory at the Biblioteca Apostolica Vaticana (Caponi lat. 260) was published by J. A. F. Orbaan in “Documenti sul barocco in Roma,” Miscellanea della R. Società Romana di Storia Patria, Roma, 1920, pp. 515-522; cf. Massimo Pomponi, “La collezione del cardinale Massimo e l'inventario del 1677,” in Camillo Massimo collezionista di antichità (Rome, 1997), pp. 91-158.

Baccicia’s oil sketch was a preparatory work for the fresco painted by him in the Algardi Chapel in Santa Maria sopra Minerva in the early 1670s, part of the program Clement X initiated in 1670 to decorate his family chapel. As noted by Angel M. Navarro in “Italian Drawings in Buenos Aires,” Master Drawings, vol. 39, no. 1 (Spring 2001)

The figures are freely distributed in the bozzetto, in contrast to the fresco, where they are hemmed in by the architectural elements framing the lunette. While the fresco shares the overall composition of the oil sketch, there are variations, such as in the number and the poses of the angels and of Christ and God the Father, who are less frontally displayed.

A drawing of the Trinity attributed to Baciccia, in pen and brown ink and grey wash, measuring 22.5 × 37 cm, was sold at auction in Paris in 2001: Etude Tajan, Hôtel Drouot, Salle 2  Paris 23/11/2001, lot 43.

Baciccia’s study drawing for the Christ figure is at the Museo de Bellas Artes in Buenos Aires (inv. no. 171). It is executed in pen and brown ink with brown wash, heightened with white, squared in red chalk and measures 237 x 187 mm. Angel M. Navarro, who was the first to identify it, comments:

The figure of Christ in the fresco is similar to that in the bozzetto and the newly identified drawing, with the exception that here his upper body is nude. The light behind the figure in the drawing, which throws it into sharp relief, suggests that early on the artist intended to include only Christ, but later adopted the present solution. The pose of the legs, the putti flying off to the right, as well as the horizontal cloudbank at the lower edge of the sheet indicate that Gaulli was already considering the architectural framework in which his fresco was to be placed, including the pediment of the altar upon which his composition would have rested.

“Italian Drawings in Buenos Aires,” Master Drawings, vol. 39, no. 1 (Spring 2001). The drawing was purchased by the museum in 1907 as part of a collection assembled in Italy in the first part of the 19th century by John Bayley.