Why are Giovanni Battista Tiepolo's Madrid ceilings considered his last major undertaking?

The Madrid ceilings are considered Giovanni Battista Tiepolo’s last major undertaking because they represent the final large-scale project he completed before his death in Spain, a country from which he never returned to Italy.1

Upon arriving in Madrid in 1762 at the invitation of King Carlos III, Tiepolo and his collaborators—his sons Giovanni Domenico and Lorenzo—spent two years decorating the Palacio Nacional. The work consisted of three ceilings: The Power of the Spanish Monarchy, The Apotheosis of the Spanish Monarchy, and Aeneas Led to the Temple of Venus.1

While these works showcased his signature bold perspective and rich chromatic orchestration, they marked the conclusion of his career as a monumental decorator. Following their completion in 1764, Tiepolo focused on other works, such as religious canvases for Aranjuez and sequences depicting the Flight into Egypt, but he did not undertake another project of the same scale or significance before his passing.1