TheVentian Republic was a major sea power and a Staging area for the Crusades, as well as a very important centre of commerce and art in the Renaissance. The city was founded as a result of the influx of refugees into the marshes of the Po estuary following the invasion of northern Italy by the Lombards in 568 . In the mid- 8th century , the Venetians resisted the empire-building efforts of Pepin III and remained subject to the Byzantine Empire , at least theoretically. As the community continued to develop and as Byzantine power waned, however, an increasingly anti-Eastern character emerged, leading to the growth of autonomy and eventual independence . Venice was a city state (an Italian thalassocracy or Repubblica Marinara , the other three being Genoa , Pisa , and Amalfi ). Its strategic position at head of the Adriatic made Venetian naval and commercial power almost invulnerable.

The buildings of Venice are constructed on closely spaced wood piles (under water, in the absence of oxygen, wood does not decay ) which penetrate alternating layers of clay and sand . Most of these piles are still intact after centuries of submersion. The foundations rest on the piles, and buildings of brick or stone sit above these footings. The buildings are often threatened by flood tides pushing in from the Adriatic between autumn and early spring . Six hundred years ago, Venetians protected themselves from land-based attacks by diverting all the major rivers flowing into the lagoon and thus preventing sediment from filling the area around the city. This created an ever-deeper lagoon environment.