St. Sebastian was commonly invoked as a protector against the plague. According to historical records, he defended the city of Rome against the plague in 680. His association with the plague could be because he survived being shot full of arrows and in pagan belief, pestilence was delivered by arrows shot by the gods above. Even Christian Romans would appreciate this symbolism. That symbolism is even captured in artwork as late as the Renaissance, where artists painted plague victims with black arrows in their body.
In artwork, St. Sebastian is depicted with arrows shot into his body, often tied to a post or a tree.