From packed train carriages to busy shopping centers, being crammed together in often poorly ventilated spaces had become so normal that it has taken us a long time to get used to social distancing. But our ancient ancestors were much more used to using airflow and space to guard against disease. Indeed, ancient Greek and Roman doctors got a surprising number of things right in this sense—even if the thinking behind their remedies was very far from what we know about how disease spreads today.