The spread of infection: AD 1346-1348

In 1346 an unusually virulent strain of plague inflicts eastern Asia and China. It seems to have elements both of bubonic plague (carried by fleas, particularly those which live on rats) and of the pneumonic variety, in which the plague bacilli are spread on the breath of infected victims.

This lethal blend of infection makes its way westwards through Asia during 1347. By the autumn of that year it affects Turkish tribes in the Crimea who are besieging Genoese merchants in a fortified trading post at Caffa (a port now known as Feodisiya). As part of their siege strategy, the Turks engage in one of history's most devastating acts of bombardment.

Instead of using their heavy catapults to lob massive stones over the walls into Caffa, they load the Siege engines with the corpses of plague victims. The terrified Genoese take to their ships, fleeing south through the Black Sea and home to Europe.

Inevitably they take with them the plague. It would have continued its relentless spread westwards without this gruesome event. But the infected cannonballs speed the disease on its way - and provide an incident which has been retold in horror ever since.

Sicily is the first part of Europe to be infected. The disease is there by October 1347. The international ports of Genoa and Venice see the symptoms in January 1348. During the rest of that year the disease spreads through most of Europe.

The towns are the hardest hit, some much more severely than others. Florence is one extreme case. The suffering of its citizens has remained particularly vivid because Boccaccio, living in the city at the time, describes the horors of everyday life and death in his introduction to the decameron.

Poisoned wells: AD 1348-1349

As Europe's citizens succumb in vast numbers to the plague, a rumour spreads that the cause lies in polluted water. The wells, it is said, have been deliberately poisoned by the Jews. The first massacres of Jews occur in France in the spring and summer of 1348. The situation rapidly becomes worse after a Jewish doctor, tortured on the rack at Chillon in Switzerland, says that he has poisoned wells with powder sent to him for the purpose by a rabbi in Spain.

Basel burns all its Jews later that month. In November the hysteria spreads to Germany.

In town after town during the next nine months, through Germany and up into Flanders, Jews are burnt in their tens of thousands (in addition to those dying anyway of the plague). Jews fleeing from this horror make their way mainly into Poland, where they are protected by the king, Casimir III. He is said to be influenced in the direction of tolerance by Esther, his Jewish mistress.

This migration brings into Poland, and subsequently into Russia, large communities of Jews speaking Yiddish - their own version of German, developed in the medieval centuries.

Northern Europe: AD 1348-1350

During 1348 the plague continues its relentless push northwards. It reaches England in the late summer, probably first by means of a ship from Calais which docks at Melcombe Regis in Dorset. A year later a ship from eastern England carries the disease across the sea to Norway. Sweden, in 1350, is the last kingdom to feel the effects.

The results everywhere are devastating. As much as a third of Europe's population dies. Economies collapse (though the wages of the survivors rise appreciably), and fear and superstition become prevalent - reinforced by several further outbreaks of plague in subsequent decades. Even including the horrors of the 20th century, the Black Death is Europe's greatest disaster.