In all these directions contagion made its way; and, doubtless, Constantinople and the harbours of Asia Minor are to be regarded as the foci of infection, whence it radiated to the most distant seaports and islands.
To Constantinople the plague had been brought from the northern coast of the Black Sea, after it had depopulated the countries between those routes of commerce, and appeared as early as 1347 in Cyprus, Sicily, Marseilles, and some of the seaports of Italy.

The remaining islands of the Mediterranean, particularly Sardinia, Corsica, and Majorca, were visited in succession.

Foci of contagion existed also in full activity along the whole southern coast of Europe; when, in January, 1348, the plague appeared in Avignon, and in other cities in the south of France and north of Italy, as well as in Spain.
The precise days of its eruption in the individual towns are no longer to be ascertained; but it was not simultaneous; for in Florence the disease appeared in the beginning of April, in Cesena the 1st June, and place after place was attacked throughout the whole year; so that the plague, after it had passed through the whole of France and Germany--where, however, it did not make its ravages until the following year--did not break out till August in England, where it advanced so gradually, that a period of three months elapsed before it reached London.

The northern kingdoms were attacked by it in 1349; Sweden, indeed, not until November of that year, almost two years after its eruption in Avignon.

Poland received the plague in 1349, probably from Germany, if not from the northern countries; but in Russia it did not make its appearance until 1351, more than three years after it had broken out in Constantinople.
Instead of advancing in a north-westerly direction from Tauris and from the Caspian Sea, it had thus made the great circuit of the Black Sea, by way of Constantinople, Southern and Central Europe, England, the northern kingdoms, and Poland, before it reached the Russian territories, a phenomenon which has not again occurred with respect to more recent pestilences originating in Asia.
Whether any difference existed between the indigenous plague, excited by the influence of the atmosphere, and that which was imported by contagion, can no longer be ascertained from facts; for the contemporaries, who in general were not competent to make accurate researches of this kind, have left no data on the subject.