Venice started off with refugees from neighboring Roman cities such as Padua, Aquileia, Treviso, Altino etc., and developed into a powerful maritime empire, a republic in it's own right.   In 1797, Venice was conquered by Napoleon Bonaparte and switched several times between being an Austrian territory,  part of the Kingdom of Italy, back to being part of Austria and eventually after the Italian Independence War of 1866 to being part of Italy.