St Marks Square (Piazza San Marco) is the principal public square of Venice, Italy, where it is generally known just as "the Piazza". All other urban spaces in the city (except the Piazzetta and the Piazzale Roma) are called "campi" (fields). The Piazzetta (the 'little Piazza') is an extension of the Piazza towards the lagoon. The two spaces together form the social, religious and political centre of Venice and are commonly considered together. It is one of the few great urban spaces in Europe where human voices prevail over the sounds of motorized traffic.
Even though the Piazza is dominated at its eastern end by the great St Mark's Basilica built in Byzantine style and its characteristic red brick bell tower called St Mark's Campanile, the Piazza's unique genius loci originates from all the building surrounding the Piazza and representing a mixture of architectural styles. Right next to the St Mark's Basilica, there is another remarkable building, the Dodge's Palace. It was built in Venetian Gothic style as the residence of the Doge of Venice and now houses a museum. Beyond that is the early renaissance Clock Tower (Torre dell'Orologio) at the entrance to the Merceria, a main thoroughfare of the city. To the left is the long arcade along the north side of the Piazza - the buildings on this side are known as the Procuratie Vecchie, the old procuracies, formerly the homes and offices of the Procurators of Saint Mark, high officers of state in the days of the republic of Venice. Turning left at the end, the arcade continues along the west end of the Piazza, which was rebuilt by Napoleon about 1810 and is known as the Ala Napoleonica (Napoleonic Wing). Across the Piazza there are also three large mast-like flagpoles with bronze bases decorated in high relief. Finally, The Piazzetta di San Marco is an open space connecting the south side of the Piazza to the waterway of the lagoon. It lies along the western facade of the Doge's Palace.
The Piazza San Marco is not far above sea level and during the Acqua Alta, the "high water" from storm surges from the Adriatic or heavy rain, it is quick to flood. Water pouring into the drains in the Piazza runs directly into the Grand Canal. This normally works well but, when the sea is high, it has the reverse effect, with water from the lagoon surging up into the Square