The Illusion of Space: St Mark's Square, Venice
plan by Robert Gatje
The fascinating thing about the piazza's design is that it is not a true square.
It is a trapezoid where one side is a little bit longer than the opposite side. This creates a space that flares out at the entry and narrows at its enclosed end. The result is an optical illusion that makes it feel like a much larger space than it is. When looking into San Marco, it appears as if one is in a massive space.
St Mark's paving adds to the illusion of depth. It was renovated during the 16th and 17th centuries and stones with a geometric pattern replaced the old bricks. The unusual pattern probably was used to mark the location of trader's stalls.
At its end, St. Mark’s Basilica thrusts into the square instead of simply forming a boundary to it. This extension breaks up the shape and imposes itself upon the scene. Very effective indeed.
A great book about this and other wonderful civic spaces is
Robert Gatje's book on Public Squares.