After the fall of Rome, Venice was the doomsday bunker of the elites. Extremely defendable position (back when cannons didn't exist), close enough to the shore to transport things and people quickly, yet far enough that it's impossible to besiege. They pooled all their money to build a city on water while everything else around them was on fire both politically and literally.
Procopius, Zosimus, Gildas, John Lydus. The Fall of Rome and the End of Civilization is a relatively recent book that consciously catalogues the bad & ugly to synthesize with the current historiography