Famed as a decorator, Tiepolo made this small sketch as his model for a vast ceiling fresco in the throne room of the Royal Palace of Madrid, a project that was the climax of his illustrious career. Taking its cue from the room's function, Tiepolo's design has as its central feature the allegorical figure of Spain enthroned and flanked by Herculean statues. Just above is the trumpeting figure of Fame. The borders are packed with lively figures representing the provinces of Spain and the continents where she held colonies. At the upper left, Christopher Columbus stands with outstretched arms on the deck of his ship. Nearby are Neptune, god of the sea, who guides the expedition, and an American Indian in a feathered headdress.
One must think of this as a design to be seen overhead in a large, high-ceilinged room. With his legendary facility, Tiepolo resolved the difficulties of foreshortening forms seen from sharply below, of deploying the figures in coherent groups, and, in turn, incorporating the groups into an effective overall design. The result is an airy sweep that seems to open directly to the heavens with all its buoyant and extravagant population paying homage to Spain.
More information on this painting can be found in the Gallery publication Italian Paintings of the Seventeenth and Eighteenth Centuries, which is available as a free PDF https://www.nga.gov/content/dam/ngaweb/research/publications/pdfs/italian-paintings-17th-and-18th-centuries.pdf