No place dazzles quite like Venice—and there's no guide more versed in its treasures than the city's premier historian, John Julius Norwich

I was lucky; I first arrived in Venice by train. It was in the summer of 1946, a week or so short of my seventeenth birthday. My parents and I had driven from Lake Garda, but they had very sensibly left the car in Mestre, because they knew how vital first impressions were and that nothing could match the excitement of walking out of the faintly Brutalist railway station straight into a Canaletto. That afternoon, my mother went off to see an old friend, and my father undertook to show me Venice. The thing to remember, he told me, was that however glorious its churches and palaces, the greatest miracle was the ensemble, the city itself. For the next two hours, therefore, we would walk through it, entering two buildings only: at the beginning, St. Mark's Basilica; at the end, Harry's Bar. That indeed was precisely what we did, and when the time came to leave and, in the gathering dusk, we took a gondola back the length of the Grand Canal, I felt that I had never left anywhere with such an aching sense of regret.

But that was more than sixty years ago. Gondolas are no longer the rather cheap taxis they once were, and anyway you'll probably arrive by air. So what about that all-important first impression? Try to get seats on the right-hand side of the plane, and not over the wing. Then, three minutes or so before landing, you will be rewarded by the perfect aerial view of Venice, laid out below you like a single, isolated jewel set in the sea, devoid of suburbs or—apart from the single causeway—of approach roads, looking almost exactly as it has for the better part of a thousand years. Not quite as good as that Canaletto, perhaps, but enough to lift the spirits in time to negotiate the new airport and the walk to your boat.

The half-hour trip to Venice across the lagoon is scenically rather less than exciting, but it should not be taken for granted—because the lagoon is the entire raison d'être of Venice. Consider it carefully, that vast expanse of marshland and shallow water (most of it would hardly reach higher than your waist), and ask yourself why anyone in his right mind would dream of building even a modest settlement, far less the most sumptuous of cities, in so uninviting a location. In fact, the reason was the only possible one: fear. The first Venetians were frightened men.

In the days of antiquity Venice did not exist; but then, in the fifth and sixth centuries, the barbarians—Goths and Huns—swept down from Central Europe into Italy, destroying everything in their path, and the panic-stricken inhabitants of the great mainland cities fled for their lives to the only available refuge, the lagoon. It might not have been very comfortable but at least it was safe. Shallow water, let it always be remembered, is a far better defense than deep: Any fool can sail over the deep, but in shallow water you have to know every eddy and current, every sandbank and shoal, or you come to grief.

And the lagoon continued to protect Venice throughout her history, separating her from the perpetually feuding cities of the mainland and encouraging her to look east instead of west—to Byzantium and the Indies and even to far Cathay (it's no coincidence that Marco Polo was a Venetian; he couldn't have been anything else)—and to build up her huge commercial empire, unique in the Middle Ages. And today more than ever we have cause for gratitude: It is thanks only to the lagoon that Venice has been spared the greatest scourge of our age, the automobile, and that the Piazza San Marco is not the most beautiful parking lot in the world.