Why does Venice have so many canals?

Canals in venice - unlike most canals those in Venice are not man made. If anything man has made the land round the canals. In the 7th Century this North Italian town was no more than a series of tiny islands and mud flats. After the fall of the Roman Empire political exiles sought refuge in the Venetian lagoons. Gradually a town emerged with many of its buildings having been constructed directly over the water supported by massive foundations on the sea bed. The canals between the groups of houses were left and consequently the only form of transport in Venice today is by boat. The vibrations of motor vehicles would soon shatter the foundations of this beautiful city which in some cases are precariously poised on nothing firmer than sand. In the days of the gondola all seemed well but the wash produced by motor boats has greatly weakened Venice's structure. To add to this historic city's problems much of the main island is slowly sinking into the sea largely because of the dredging and water pumping activities of a nearby industrial area. The Italian government has now embarked on the difficult project of trying to keep this marvel of medieval and renaissance architecture and engineering afloat.