Very interesting quiz, but if you ask for the Dardanelles then you should also accept the Bosphorus (why does this come up so frequently?). Also you could change the hint to "Former main/biggest/most known Italian maritime republics": there were more than two, in Italy we usually group together the four most important, which were Venice, Genoa, Pisa, and Amalfi. Though I realise most people will guess the biggest ones first anyway
a little long