In May 1347, the little convoy of early homebound Genoese and Venetian galleys from Kaffa had spread the Black Death widely along the sea lanes. They had spread it on the western coast of the Black Sea (and the eastern Balkans) to Constantinople and further to a string of islands and seaports along the sea lanes of the western Aegean Sea to the Venetian fortified supply points of Corone and Modon (Koroni, Methoni) on the south-western tip of the Greek mainland, and to Crete. Then, the Venetian galleys disappear from the sources. This sudden silence in the sources clearly indicates (but does not prove) that these Venetian galleys were incapacitated by the Black Death and could not sail further.

This changed abruptly with the return voyage of the main convoy from Kaffa in the autumn as the homebound Venetian fleet of galleys moved northwards along the coast of Dalmatia (present-day Croatia) and exposed these parts of the western Balkans to the Black Death. At the time, many of the islands off the coast and some port towns on the coast belonged to or were controlled by the Republic of Venice, and a number of other small seaport towns were used as harbours of convenience. According to the chroniclers, a string of such locations on the Dalmatian coast had outbreaks of the Black Death around the turn of the year: Ragusa (Dubrovnik), Spalato (Split), Traù (Trogir), Sebenico (Šibenik) and Zara (Zadar). At first glance, it would seem that the Black Death first went ashore in Spalato where the outbreak was noticed on Christmas Day 1347 and was still raging on 23 March. One should note that average temperatures in the months November–March are close to or over 10ºC, hence the epizootic and epidemic processes would function throughout this period with temperatures slightly over the average. In Ragusa (Dubrovnik), the presence of the Black Death was noted before 13 January. Taking into account that chilly late autumn or early winter weather must have slowed down the enzootic and endemic developments leading to the terrifying recognition that the Black Death was present, this implies that Spalato probably was contaminated in early November. Ragusa had become infected a little earlier because it was a much larger urban centre.