Adjacent and connected to the Doge's Palace on Piazza San Marco, St. Mark's Cathedral is the most prominent church in Venice.  It is a notable example of Byzantine architecture, based on a Greek Cross floor plan and surmounted by five domes.  The most likely influence on its design was the Hagia Sophia in Constantinople (Istanbul). 

The original St. Mark's dates to 832.  This one burned in 976, was rebuilt in 978 and then the present basilica begun in 1063, was completed in 1071.  It is likely that both Byzantine and Italian architects were employed in the construction and decoration.  The basilica was consecrated in 1094, the same year the body of St. Mark was supposedly rediscovered in a pillar of the church.  There have been additions and alterations over the centuries.  Over each exterior arch, are rich mosaics from different periods. 

The 4 Bronze Horses of St. Mark, on the facade of the second floor above the central doorway, were installed on the basilica about 1254.  They date back to ancient Rome and by some accounts, once adorned the Arch of Trajan in the Roman Forum.  For a long time they were part of the Hippodrome in Constantinople.  In 1204 the Doge sent them back to Venice as part of the loot sacked during the Fourth Crusade.  They were taken by Napoleon in 1797 but restored in 1815.  They remained above the central doorway until 1990, when they were removed to an exhibition room because the harsh environment of Venice was deteriorating them.  The horses now on the facade of the cathedral are fiberglass models of the originals.

The interior is rich with mosaics, ceremonial objects, and sculpture.  Seldom did a Venetian ship return from the Orient without bringing "something" taken or looted from some ancient building, to add to the basilica.