The Black Death was a devastating global epidemic of bubonic plague that struck Europe and Asia in the mid-1300s. The plague arrived in Europe in October 1347, when 12 ships from the Black Sea docked at the Sicilian port of Messina.
People gathered on the docks were met with a horrifying surprise: Most sailors aboard the ships were dead, and those still alive were gravely ill and covered in black boils that oozed blood and pus.

Sicilian authorities hastily ordered the fleet of “death ships” out of the harbor, but it was too late: Over the next five years, the Black Death would kill more than 20 million people in Europe—almost one-third of the continent’s population.
Indeed, in the early 1340s, the disease had struck China, India, Persia, Syria, and Egypt.

The plague is thought to have originated in Asia over 2,000 years ago and was likely spread by trading ships, though recent research has indicated the pathogen responsible for the Black Death may have existed in Europe as early as 3000 B.C.
Europeans were scarcely equipped for the horrible reality of the Black Death.

Today, scientists understand that the Black Death, now known as the plague, is spread by a bacillus called Yersina pestis. (The French biologist Alexandre Yersin discovered this germ at the end of the 19th century.)

They know that the bacillus travels from person to person through the air, as well as through the bite of infected fleas and rats. Both of these pests could be found almost everywhere in medieval Europe, but they were particularly at home aboard ships of all kinds—which is how the deadly plague made its way through one European port city after another.

No one knew exactly how the Black Death was transmitted from one patient to another, and no one knew how to prevent or treat it.
Because they did not understand the biology of the disease, many people believed that the Black Death was a kind of divine punishment—retribution for sins against God such as greed, blasphemy, heresy, fornication and worldliness.