What is is called when illusionistic ceiling paintings employ a technique that means “to fool the eye”?

The Pitti Palace in Florence, Italy, illustrates this
technique of trompe de l'oeil [in French it literally means
mistake the eye, and sometimes the de, meaning
of, is omitted].  Built during in the 1300s, a century before the
beginning of the Renaissance, this impressive example of the illusionary technique
has walls that seem absolutely three-dimensional with false balconies at the tops of
these walls, statues that are really part of the murals.  Even false sculptures over
doorways decorate the walls.

This artistic technique was
economical and useful as it created dimension and structure without the cost. For
instance, in Guercino's Aurora, 1621-23, the addition of towering illusionistic
piers--even a ruined one at one end of the ceiling--makes a more impressive
picture.