Trade routes and plague transmission in pre-industrial Europe

Abstract

Numerous historical works have mentioned that trade routes were to blame for the spread of plague in European history, yet this relationship has never been tested by quantitative evidence. Here, we resolve the hypothetical role of trade routes through statistical analysis on the geo-referenced major trade routes in the early modern period and the 6,656 geo-referenced plague outbreak records in AD1347-1760. Ordinary Least Square (OLS) estimation results show that major trade routes played a dominant role in spreading plague in pre-industrial Europe. Furthermore, the negative correlation between plague outbreaks and their distance from major trade ports indicates the absence of a permanent plague focus in the inland areas of Europe. Major trade routes decided the major plague outbreak hotspots, while navigable rivers determined the geographic pattern of sporadic plague cases. A case study in Germany indicates that plague penetrated further into Europe through the local trade route network. Based on our findings, we propose the mechanism of plague transmission in historical Europe, which is imperative in demonstrating how pandemics were spread in recent human history.

Figure 1

Spatial distribution of plague outbreak in Europe, and Northern Africa, AD1347–1760. Plague outbreaks are related to the patterns of trade routes, both overland and maritime, and also major trade ports in pre-industrial Europe. Cities with recorded plague outbreaks are marked with red dots, with the size of dots referring to the number of plague outbreak during the study period (See legends). The blue lines indicate the major trade route in early modern Europe. The black dots identify the locations of major trade ports with plague outbreak over the study period. Major trade ports without plague outbreak over the study period are labeled in grey dots. Trade routes and trade ports at countries with no plague record are omitted. From our results, more plague outbreaks happened in the periphery of trade routes and trade ports. The map is generated in ArcGIS version 10.1 (www.esri.com/software/arcgis).

Figure 2

Sporadic plague outbreak (N < 5) did not follow the pattern of major trade routes. The red spots represent the locations of sporadic outbreak of plague (856 locations). The blue lines indicate the major trade route within our study period. The black dots identify the major trade ports with plague outbreak. The trade ports with no reported plague outbreak within our study period are labeled in grey dots. The map is generated in ArcGIS version 10.1 (www.esri.com/software/arcgis).

Figure 3

Distribution and frequency of plague outbreak in relation to the local Holy Roman Empire trade route in Germany, AD1347–1760. It can be seen that locations with more plague recurrence (as referred by the size of red dots) are closer to the local Holy Roman Empire trade route (blue lines). The strength of recurrence fades in according to the distance away from these trade routes as suggested by the statistical analysis (Table 3). The map is generated in ArcGIS version 10.1 (www.esri.com/software/arcgis).

Figure 4

Possible plague spreading pattern from port to inland in Europe, AD1347–1760. Plagues were carried from other permanent plague focus to major trade ports in Europe. The contagion will go further to the hinterland by major trade routes or navigable river connecting the major trade ports. By transporting through the major trade route, the contagion will eventually focus at major trade node, resulting in the formation of plague hotspot in historical Europe. The pathway from major trade route to plague hotspot would also pass through local trade route. Certain amount of contagion would enter nearby navigable rivers from major trade route or major trade node. The navigable rivers would further carry the contagion inland and create sporadic cases all over the European continent.