The use of demographic data about cardinal mortality drawn from Salvador Miranda’s “Cardinals of the Holy Roman Church” archive confirms and quantifies the greater vulnerability of northern Europeans to Rome’s malarial fevers relative to their Roman counterparts. Non-Italian visitors to Rome suffered about three times the rate of malaria deaths as did Italians and Greeks, who had acquired various defenses against malaria. Northern Italians were far less susceptible than expected to Rome’s malarial fevers, however, whereas Iberian visitors to Rome were far more so. The eventual decline of malaria in Rome was not so much a function of climate change as of Rome’s steady post-1600 population growth.