Sebastian was a Roman officer of the imperial guard. He tried to help two of his Christian friends, Marcus and Marcellianus, who were sentenced to death because of their beliefs. In the process, he converted many other Christianity. He was later discovered and sentenced to be shot with arrows. However, the wounds did not kill him. When Irene, the widow of one of his former converted fellow, came to bury him, she found him still alive and took him to her lodging and cared for him. 

Mantegna depicted the moment after the shooting. In this scene, Sebastian turns his beseeching gaze heavenwards. The halo indicates he has become a saint. His slightly twisted body and torturous visage reminds me of Michelangelo's dying slave, which both express some degree of sensuality. In comparison to the dying slave, Mantegna's Sebastian provokes more of a sense of masochism instead of inner struggle. Part of the reason that Mantegna creates this painting is because the ancient Greeks believed that Apollo caused diseases with his arrows, and the recurring plagues in 15th century led to dozens of works on the St Sebastian theme. 

Mantegna includes classical Roman architecture elements in this painting. Their ruined state implies that with the triumph of Christianity, the Roman empire was coming to an end. In addition, Mantegna perfectly unifies his signature into the painting by depicting the line on the column, which says in Greek letter "The work of Andrea." By doing so, Mantegna presents himself as an expert of Hellenic antiquities, which parallels the Renaissance idea of individualism.