This map - from Germany's Federal Ministry of Education and Research - depicts the route of travel (and the years of the plague's arrival) throughout Europe).
Plague bacteria had caused significant epidemics before. The famous Roman emperor, Marcus Aurelius, reportedly died from it in the 2nd century. Lying dormant for a time, it erupted again in the 1320s, most likely in the Gobi Desert.
By 1333 Black Death had reached the northeastern province of China. Millions of people died. The disease spread rapidly throughout the rest of Asia, and into the Crimea, along established trade routes.
Ships leaving the Crimean Peninsula town of Kaffa (formerly known as Theodosia and today as Feodosiya, Ukraine) were normally loaded with the goods which fourteenth-century Europeans wanted. By 1346, Black Death had invaded this Black Sea port (which is near Yalta, the town made famous by Churchill, Roosevelt and Stalin during World War II).
Sailors, wanting to leave what had become a city of death, boarded four ships bound for Messina, Sicily. By the time the ships reached their port of call, however, many sailors were dead. Black rats, common ship stowaways, most likely infected the crew.
The people of Messina greeted ships manned by a few dying men who were clinging to the oars. The rest of the crew was already dead. Horrified, residents of the Sicilian town turned the ships away, but the damage was already done. The pestilence had reached Europe. It was 1347.
When the ships reached Genoa, the bacteria was ready to pounce on the heart of Europe.