Venice survived the invasions mainly because it was a protectorate of Byzantium, because the natural swamps around Venice gave it a natural moat or defense, and because of the persistence and stability of the Venetian people and government. 

Here we see the early medieval cathedral of Saint Mark with its Byzantine style and inherent attractiveness. 

The Venetian Bridge of Sighs created an influential style. This, the original, was named so because on one side of the bridge was the high court, i.e., where capital punishment could be meeted out. On the other side was the place of execution. A prisoner about to die was marched across the bridge and he could see, through the windows, the open sea on one side and the quaint canal on the other, before meeting his Maker. What heartfelt sighs that bridge has heard over the years! 

There are copies of the Bridge of Sighs at Oxford and Cambridge Universities -- were final exams held on the other side of these?....