"...this solitude was anciently chosen by man for his habitation.  They little thought, who first drove the stakes into the san and strewed the ocean reeds for their rest, that their children were to be the princes of that ocean, and their palaces its pride;... Had deeper currents divided their islands, hostile navies would again and again have reduced the rising city into servitude; had stronger surges beaten their shores, all the richness and refinement of the Venetian architecture must have been exchanged for the walls and bulwarks of an ordinary seaport.  Had there been no tide.. the narrow canals of the city would have become noisome, and the marsh in which it was built pestiferous.  Had the tide been only a foot or eighteen inches higher in its rise, the water-access to the doors of the palaces would have been impossible... Eighteen inches more of difference between the level of flood and ebb would have rendered the doorsteps of every palace, at low water, a treacherous mass of weeds and limpets, and the entire system of water-carriage for the higher classes, in their easy and daily intercourse, must have been done away with.  The streets of the city would have been widened, its networks of canals filled up, and all the peculiar character of the place and the people destroyed."

John Ruskin, The Stones of Venice.

The Rough Guide Venice and Veneto -- Up to the usual Rough Guide standards, this is a great introduction to Venice.  Its restaurant and hotel suggestions are good, but it really shines in describing the city, and offering suggestions for many days' walks