The Trevi Fountain is a great example of solids contrasting with open cavities. To get to the fountain, you move down narrow streets, compressed by solid walls. Then, suddenly, the massive walls open. Daylight explodes onto a park, where the fountain in the center sends water splashing over natural, uncut boulders that contrast with the cut stone buildings all around.
SOLIDS AND CAVITIES
“Every drawing begins with the shadow.”
Notice how all the dark areas (shadows in the building behind Trevi Fountain) define the shapes of the solids.
From Experiencing Architecture by Steen Eiler Rasmussen
From 17 Itinerari a Roma by Francois Nizet
The Church of Santa Maria della Pace and Palazzo Massimo alle
Colonne are shown above. Maria della Pace is a wild contrast of solid forms bulging
into a small courtyard. The palazzo appears to be very solid and heavy on top, and a dark cavity
is carved out of its base behind a row of slender columns that jump out from the darkness of the opening.