David P. Clark

“strangely, on the verge of storming Rome itself, Attila withdrew. Why? For many centuries the official answer was that God had intervened in some mysterious way to protect his chosen city, Rome, seat of the papacy. In more recent times, such supernatural explanations have fallen out of favor and the question has arisen anew. Some have suggested that Attila was overawed by the sanctity of Rome. But why would a pagan warlord like Attila stand in awe of a Christian center? Attila was by no means an ignorant barbarian: For example, he invited Roman and Greek engineers into Hun territory to install bathing facilities. However, his respect for Roman civilization was clearly of a pragmatic rather than a religious nature. Another theory is that Attila was worried about leaving unattended his newly acquired homeland, in what is now Hungary. But then why did he venture out almost as far as Rome and hang around indecisively for so long before returning? All these explanations founder on the same point. It seems clear that Attila did indeed set out with every intention of taking Rome, but his expedition came to a premature halt. Mounting modern evidence suggests that Attila was stopped by a virulent epidemic of dysentery, or some similar disease. Most of his men were too ill to stay on their horses, and a significant number died. In short, bacteria saved Rome.”
― David P. Clark, Germs, Genes, & Civilization: How Epidemics Shaped Who We Are Today