Port cities acted as epicenters for the Black Death’s transmission in medieval Europe. These epicenters were infected through shipping connections with Eurasia as Italian merchants fled Kaffa. Although the plague also traveled over land, ships were the primary vehicles of transport, allowing the Black Death to make numerous metastatic leaps, as it did when it entered Weymouth in England by ship from France and then jumped to Norway through the grain trade that departed Weymouth. These leaps “greatly hastened the Black Death’s conquest of Europe, and, arguably, made the almost total success of the European campaign possible” (231). The average rate of transport by ship was 40 kilometers per day, while overland plague traveled roughly two kilometers per day. Thus, the plague had the ability to travel more swiftly by sea. Furthermore, the slow pace at which the plague spread by land, according to the epidemiological evidence outlined above, confirms that the Black Death was bubonic, not pneumonic, plague because the latter would have spread more swiftly.

Pace of spread and population density also interacted to affect the dynamics of plague’s spread. As the author notes, “high population density […] increased the pace of spread along communication lines,” but it also “slowed down the pace of conquest” (231) due to the time required for the illness to reach epidemic levels in a larger population.