The Piazzetta di San Marco is, strictly speaking, not part of Piazza San Marco but an adjoining open space connecting the south side of the Piazza to the waterway of the lagoon.

The Piazzetta is marked by two large granite columns carrying symbols of the two patron saints of Venice. The first is Saint Theodore, who was the patron of the city before St Mark. The second (eastern) column has a creature representing a winged lion — the Lion of Venice — which is the symbol of St Mark. This has a long history, probably starting as a winged lion-griffin on a monument to the god Sandon at Tarsus in Cilicia (Southern Turkey) about 300 BC.

Piazza San Marco (St Mark's Square) is the principal public square of Venice, where it is generally known just as la Piazza ("the Square"). It is unique among the squares of European cities. It is located in the center of the city, but it is not as noisy as traffic in other squares, thanks to the waterway traffic in Venice. The 19th century French emperor Napoleon once praised it as "the most beautiful living room in Europe".

The history of the Piazza San Marco can be conveniently covered in four periods, but the only pre-renaissance buildings and monuments still standing there are St Mark's, the Doge's Palace and the two great columns in the Piazzetta. The Square is dominated at its eastern end by the St Mark's Basilica. It is described here by a perambulation starting from the west front of the church (facing the length of the Piazza) and proceeding to the right.

The Campanile of St Mark's church is standing free in the Piazza. Adjacent to the Campanile, facing towards the church, is the elegant small building known as the Loggetta del Sansovino, used as a lobby by patricians waiting to go into a meeting of the Great Council in the Doge's Palace and by guards when the Great Council was sitting.