Focus on context: disease and demography

The Tartars [Mongols of the Golden Horde] set on [attacked] a Genoese trading station in the city of Tana and chased the merchants to their redoubt [fort] at Caffa… a town on the Crimean coast which the Genoese had built and fortified as a base from which to trade with the [East]...Their plans were disastrously disturbed by the plague which was soon taking heavy toll of the besiegers…[F]ew places are so vulnerable to disease as a besieged city and it was not long before the plague was as active within the city as without… [The Genoese] took to their galleys and fled from the Black Sea towards the Mediterranean. With them travelled the plague.

One of the main trade routes by which the spices and silks from the East reached the European market was by way of Baghdad and then along the Tigris [River] and through Armenia to the entrepot [trading] stations of the Italian merchants in the Crimea. Nothing is more likely than that the plague should travel with the great caravans and spread itself among the [Mongols] of the Crimea.