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.

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.

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.

Venice, which has the skills to provide the transport and an already established trade concession, is once again perfectly placed.

But it soon meets strong rivalry from two other great maritime communes, Genoa and Pisa.