The Rage of the Dog Star: Spatio-Temporal Risk of Malaria in the Eastern Mediterranean During the Crusader Period (c. 1000–c. 1250)

Multiple forms of endemic malaria existed in the Mediterranean Basin from the 3rd millennium BCE until eradication regimes were imposed in the 20th century, with major societal health impacts across the history of the region. Little attention has been paid to the role endemic malaria played during the high medieval period, especially during the Crusades, when large Christian armies transited the Mediterranean to conquer the Levant, forging new states, trade lanes and pilgrimage routes in the process. This study utilizes a recent GIS-enabled malaria risk model validated for the pre-modern Mediterranean to re-evaluate contemporary accounts of illness and epidemics in the Crusader Levant. While medieval sources often provide ambiguous descriptions of disease, careful consideration of these accounts in light of the demonstrable spatial and temporal risk of malaria infection provides substantial evidence of these kinds of epidemics. The resulting evidence suggests that several malaria species, either on their own or in concert with other pathogens, afflicted numerous Crusade campaigns in low-lying landscapes during the warmest periods of the summer and fall in the Levant. In turn, these malaria epidemics had a major impact on the history of the Crusades and the Crusader States.