The reign of Roman disease: why did disease hit a flourishing empire?

The second century AD, says Harper, could be considered the height of the Roman empire – what historian Edward Gibbon has famously called the “happiest age”. With a booming population, mass urbanisation and trade links stretching out from Africa to East Asia bringing in aromatics, spices and silks, the empire was flourishing. But, around this time, it also faced many outbreaks of infectious diseases, including the infamous Antonine Plague (165–80 AD), also known as the Plague of Galen. We know that major pandemics such as this were a powerful factor in influencing Roman history.

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Yet the combination of illness and success strikes a strange note. Harper argues that we should consider history from the ecologist’s point of view, seeing how pandemics have affected us and emphasising how our actions have affected them. Doing so can reveal how progress has long had a complicated relationship with disease. Unlike what might be expected, disease outbreaks do not just occur because a society is in crisis, or because of misery and trouble.

Disease can also thrive as a result of conditions of human social development. The great diseases of the world are, in a sense, evolutionary responses to the way we live, says Harper, and have changed the physical environment around us. They are caused by agents or microparasites (usually either bacteria, fungi, protozoa or viruses). These are rewarded, argues Harper, “if they happen to be good at getting energy or taking over cells and passing their genes on to future generations”. These parasites benefit when their host benefits; when humans multiply and travel, it creates opportunities for them.

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Not only did the increasing population size and the urbanisation of the Roman empire mean that there were great numbers of people sharing air, water and sewage space, but the large size and interconnectedness of the empire created the perfect conditions for the population to be exposed to new pathogens and for disease to spread rapidly. With the Roman empire facing such success, outbreaks were bound to happen.

Kyle Harper is the author of Plagues Upon the Earth: Disease and the Course of Human History (Princeton, 2021)

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