Venice's long link with Constantinople is evident in the mosaics, in the Byzantine style, for which the islands of the lagoon are famous.
The earliest are on Torcello, the first centre of the Venetian state, where the cathedral apse contains a superb 13th-century image of the Virgin and Child.
Two developments in the 11th century prove of lasting benefit to Venice, which is by now the leading maritime power in the Adriatic.
The first is the appearance of a rival in Italian waters.
Reforms are put in place to ensure that the position of the doge (who holds office, like the pope, until death) cannot evolve into that of a hereditary signore - as will subsequently happen in other Italian communes.
In various stages between 11 the government of Venice (which now includes Venetian colonies along the Dalmatian coast) is removed from the sole personal responsibility of the doge and is transferred to powerful councils.
A Council of Ten is added in 1310, to check on everybody else.
The Italian communes of the west coast demonstrate their strength in the 11th century when Genoan and Pisan fleets, often working in alliance, protect Corsica and Sardinia from the depredations of Muslims.
Both cities subsequently develop extensive trade in the western Mediterranean.
Dating mainly from the 12th and 13th centuries, these Italian mosaics represent the culmination of a great Byzantine tradition.
But at the end of the 13th century Italy also provides a new beginning in an equally great theme in the history of art - that of the European fresco.