Sebastian, Saint (d. A.D. 288), early Christian martyr. Stories about him are mostly legends. According to these legends, Sebastian joined the Roman army with the intention of helping Christians. He became popular with Emperor Diocletian, who made him a military commander. When his religious faith was discovered, Sebastian was tied to a tree and shot with arrows. Left for dead, he recovered only to be captured later and put to death in the Roman amphitheater. Scenes of his martyrdom were popular subjects of early Italian painters. His feast day is January 20.