More In depth on the plague

The Black Death was one of the most devastating pandemics in human history, peaking in Europe between 1348 and 1350. Although there were several competing theories as to the etiology of the Black Death, recent analysis of DNA from victims in northern and southern Europe indicates that the pathogen responsible was the Yersinia pestis bacterium, which causes the Bubonic plague, although these were different, previously unknown ancestral variants of those identified in the 20th century.

The Black Death is thought to have started in China or central Asia, before spreading west. It is estimated to have killed 25 million people or 30% of the population of China. The plague then traveled along the Silk Road and reached the Crimea by 1346. From there, it was probably carried by Oriental rat fleas living on the black rats that were regular passengers on merchant ships. Spreading throughout the Mediterranean and Europe, the Black Death is estimated to have killed 30–60 percent of Europe's population. All in all, the plague reduced the world population from an estimated 450 million to between 350 and 375 million in the 14th century.

The aftermath of the plague created a series of religious, social and economic upheavals which had profound effects on the course of European history. It took 150 years for Europe's population to recover. The plague reoccurred occasionally in Europe until the 19th century.

Major outbreaks

There have been three major outbreaks of plague. The Plague of Justinian in the 6th and 7th centuries is the first known attack on record, and marks the first firmly recorded pattern of bubonic plague. From historical descriptions, as much as 40 percent of the population of Constantinople died from the plague. Modern estimates suggest half of Europe's population was wiped out before the plague disappeared in the 700s. After 750, major epidemic diseases did not appear again in Europe until the Black Death of the 14th century. The Third Pandemic hit China in the 1890s and devastated India, but was confined to limited outbreaks in the west.

The Black Death originated in or near China and spread by way of the Silk Road or by ship. It may have reduced world population from an estimated 450 million to between 350 and 375 million in 1400.

The plague is thought to have returned at intervals with varying virulence and mortality until the 18th century. On its return in 1603, for example, the plague killed 38,000 Londoners. Other notable 17th-century outbreaks were the Italian Plague (1629–1631); the Great Plague of Seville (1647–1652); the Great Plague of London (1665–1666); and the Great Plague of Vienna (1679). There is some controversy over the identity of the disease, but in its virulent form, after the Great Plague of Marseille in 1720–1722, the Great Plague of 1738 (which hit Eastern Europe), and the Russian plague of 1770-1772, it seems to have gradually disappeared from Europe. By the early 19th century, the threat of plague had diminished, but it was quickly replaced by a new disease. The Asiatic cholera was the first of several cholera pandemics to sweep through Asia and Europe during the 19th and 20th centuries.

The 14th-century eruption of the Black Death had a drastic effect on Europe's population, irrevocably changing the social structure. It was, arguably, a serious blow to the Catholic Church and resulted in widespread persecution of minorities such as Jews, foreigners, beggars, and lepers. The uncertainty of daily survival has been seen as creating a general mood of morbidity, influencing people to "live for the moment", as illustrated by Giovanni Boccaccio in The Decameron (1353).