This fresco, one of four, was commissioned by Cosimo I de' Medici and his wife, Eleanor of Toledo, to adorn the walls of Eleonor's private chapel in the Palazzo Vecchio in Florence. Three of the four chapel walls painted by Bronzino depict the story of Moses. The fresco The Crossing of the Red Sea is found on the south wall of the chapel. Art historian Liana De Girolami Cheney has speculated that "perhaps this painting constitutes the best expression of Bronzino's Maniera [Mannerism] style in its combination of sensuality and capriciousness".
The fresco includes multiple biblical scenes. The figures at the center and left of the foreground represent the Hebrews preparing for exodus from Egypt (Exodus 12:33-39), while those in the background represent the Hebrews having safely crossed the Red Sea. The figure in blue in the background, Moses, is gesturing for the waters to return to normal and, in the process, drown the Egyptians who are pursuing the Hebrews (Exodus 14:21-29). An aged Moses appears again in the right-hand foreground, with a brown robe, grey beard, and two rays of light radiating from his head, placing his hand on Joshua and instructing him to take over as his successor, to lead the Israelites to the promised land (Numbers 27:12-23).
The topless male figure at the left of the foreground, who is awkwardly contorted and grasping the wrist of the seated female, is posed with his hip thrust outward in an exaggerated fashion, and one arm raised upward, which are typical elements of Mannerist positioning. In fact, the standing, topless male figure's pose is believed to have been inspired by the Idolino, a Roman copy of a Greek bronze statue discovered in an excavation of Pesaro in 1530, where Bronzino happened to be working at the time. Also, the male figure in the center who is leaning against a rock is shown with one leg crossed behind the other. It was a pose frequently used by Bronzino and ranks thus as something of an authorial motif.
Concealed within the fresco, meanwhile, are several references to the Medici's dynastic and political aims. For instance, Moses here represents Cosimo I de' Medici who aimed to lead his people to glory. This connection is boldly reinforced by the red Egyptian banner at the left of the background which shows a partial coat of arms of the Strozzi family. This feature alludes to the Battle of Montemurlo in 1537 at which the Cosimo defeated their fierce rivals (the Strozzi's). Additionally Moses' nomination of Joshua as the Hebrews' future leader in the foreground, combined with the presence of the pregnant and nursing women in the image, alludes to the birth of Cosimo I's son Fernando, who was heir apparent to the ducal state.
Art historian Deborah Parker notes that these frescos "demonstrate Bronzino's masterful use of colour, his handling of 'ombre' and 'lumi' - shadows and light to create relief. The jewel-like palette is ravishing: Bronzino used intermediate hues such as violet, ultramarine, coral, soft yellows, a wide range of greens rather than the more common saturated red and blue seen, for example, in Raphael's paintings. the combination of colours in applications of cangiatismo (or colour changes in which two colours are juxtaposed) is no less striking [...] This ornamental use of colour exemplifies the decorative artificiality of Maniera painting".
