Although it is as well established as anything can be that Christopher Columbus was born in Genoa, there has been a lot of foolish speculation about his nationality, particularly by those hoping to claim him for their own. In this debate, the question is often raised: why didn't he ever write anything in Italian?
Well, for a start, most of his most important correspondence was when he was resident in Spain, and writing to people who spoke Spanish. However, one commentator has pointed out something that would have been as obvious to his contemporaries as it is forgotten today: his native language was not Italian; it was Genoese! Genoese is not a dialect of Italian; it is a dialect of Ligurian. It is as different from Italian as Occitan/Provençal is from French.
Over the last few centuries the centralisation of political power has also meant the centralisation of national languages, leaving the regional languages to wither on the vine. However, they were still very much alive five centuries ago. Indeed, Italy itself did not exist then as a political entity. Genoa in those days was one of many independent republics which patterned northern Italy at the time like a big jigsaw puzzle.
Genoese is not dead yet, but it is withering on the vine. In a couple of centuries it will be forgotten, and people will still be asking why Columbus never wrote in Italian.
Reference: Paolo Emilio Taviani, Cristoforo Colombo, Genius of the Sea (2nd edition, 1991)