“There are observances necessary for a healthy man to employ during a pestilence,” advised the first-century Roman medical writer Aulus Cornelius Celsus, “although in spite of them, one cannot be secure.” Best of all is “to go abroad, take a voyage. When this cannot be, to be carried in a litter, walk in the open before the heat of the day, gently, and to be anointed in like manner.”