Seeking refuge from mainland invaders, Venetians first settled on these lagoon islands in 421 AD eventually becoming the richest city in the world and a dominant naval power. Today, while the main island of Venice remains the centerpiece, the outer islands have retained their individual identities and remain fascinating stops on any visit to Venice. Follow Karine Hagen of Viking Cruises as she tours Torcello, San Giorgio Maggiori, Sant Erasmo, Burano, Murano and Lazzaretto Nuovo.