Note the bronze men (Moors) that mark the top of each hour - a worker was knocked off the clock in the 17th century by the moving Moors falling to his death.  You can take a tour inside the clock and tower. 

 Entrance to the main shopping area called the Mercerie.  

St Mark's Clocktower bell was made in 1497. 

St Mark's Clocktower

The Clock Tower in Venice is an early renaissance building on the north side of the Piazza San Marco at the entrance to the Merceria. It comprises a tower, which contains the clock, and lower buildings on each side. It adjoins the eastern end of the Procuratie Vecchie. Both the tower and the clock date from the last decade of the 15th century, though the mechanism of the clock has subsequently been much altered. It was placed where the clock would be visible from the waters of the lagoon and give notice to everyone of the wealth and glory of Venice. The lower two floors of the tower make a monumental archway into the main street of the city, the Merceria, which linked the political and religious centre (the Piazza) with the commercial and financial centre (the Rialto). Today it is one of the 11 venues managed by the Fondazione Musei Civici di Venezia.

• http://en.wikipedia.org/wiki/St Mark's Clocktower
• Page 883 - Steves, R., 2014, Best of Europe 2015: Perseus Books Group, Berkeley, 1385p.