The history of Venice is based on a paradox: a few islands in the northwest Adriatic, surrounded by mud, gave birth to the capital of a maritime and commercial empire and the largest port of the Middle Ages. Placed at the bottom of the deepest gulf of the Mediterranean, on the banks of two great Italian rivers, the Po and the Adige, which leads to the Brenner Pass, the lowest point in the Alps, the town emerges in the ninth century.