The Baroque illusionistic ceiling technique using perspective is called quadratura.
Quadratura makes a flat or vaulted ceiling appear to continue into an imaginary architectural space. Painters used carefully calculated perspective, foreshortening, painted columns, arches, balconies, and openings to create the impression of deep space or a heavenly sky above the viewer.
The term is closely related to trompe-l’œil, but the two are not identical. Trompe-l’œil is the broader idea of deceiving the eye, while quadratura specifically emphasizes architectural illusion organized through perspective. Earlier ceiling experiments used techniques such as di sotto in sù, or “seen from below,” and Baroque artists developed these effects into elaborate theatrical environments.
Andrea Pozzo’s ceiling and dome designs at Sant’Ignazio in Rome are among the best-known examples.