Praised be Jesus and Mary, now and forever.
St. Sebastian was a victim of the persecution of Diocletian, which was the last and greatest before Christianity was legalized. However, he may have died in a more isolated incident before the great persecution broke out. Historically, certain information about St. Sebastian that is historically certain is limited. Most of what is told about him comes from an account that is historical fiction rather than history. It was written about a century and a half after his death. It tells his story using a few facts that are certainly true, other things that are certainly false, and many things about which it is hard to be certain.
The most certain facts are those which St. Ambrose tells us, writing earlier. First of all, St. Sebastian was of Milanese origin. This could mean that he was born in Milan, or, as the Greek and Latin legends say, he was born of a Milanese mother in Narbonne, on the southern coast of present-day France. Second, he died at Rome, which is where he was also buried, in the catacombs that are now called by his name. St. Ambrose says that he may have gone to Rome because the persecution in Milan had either ended or was not very intense at that time. At Rome, on the other hand, there was a bitter persecution raging due to the zeal with which the faith was practiced. And so there he would have a better chance to prove his loyalty to Christ.
Now we come to what the story of his passion has to say about him. And as I said, this is historical fiction. When someone writes a story like this about a saint or makes a movie, things are made up and added to the facts in order to fill out the story in a way that is supposed to give an idea of what the saint was like. Some historians would like us to discard the whole thing because the information is not certain. But the liturgy invites us to learn from it, for it had us pray for a spirit of fortitude, so that, "taught by the glorious example of your martyr St. Sebastian, we may learn to obey You rather than men." If we were only to consider the few facts that St. Ambrose wrote, we wouldn't have much of an example, and we would have nothing about how St. Sebastian obeyed God rather than men.
In the story, St. Sebastian is a soldier. This is almost certainly true because when the story was written, St. Sebastian was already being venerated and had a liturgical feast. His profession was a very basic fact, so it would have been known, and this would have been one of the elements that the author used. We are told that he was brave and loyal, and this caused him to rise through the ranks and become the commander of the emperor's guards in Rome. There are historical problems with this part of the story, but let's take it as a way of illustrating the saint's character. Because he held this position, he had access to Christians who were imprisoned for their faith. He was able to encourage many of them to remain faithful unto death, so as to inherit the crown of life. He also led many pagans to embrace Christianity.
There's no doubt that the number of Christians was growing rapidly in those decades. This was one of the things that motivated the persecutions. And so, if a fervent Christian like St. Sebastian spent a while in Rome, he would have led others to the faith. According to the story, St. Sebastian's evangelization and assistance to the martyrs were discovered, and he too was charged with being a Christian. Brought before the emperor, he remained firm in the faith, and so was sentenced to death. A group of soldiers took him out to a field, tied him to a pole, and shot him with so many arrows that he looked like a hedgehog, as the story goes. They left him for dead.
During the night, Irene, widow of the martyr St. Castulus, who was supposed to be one of the martyrs that St. Sebastian had helped, the widow of this martyr came to carry the holy body off for burial. But she was surprised to find that St. Sebastian was still alive. She took him home and nursed him back to health in her house on the Palatine Hill, not far from the emperor's palace. St. Sebastian's recovery was prodigiously fast. It only took a few days. His fellow Christians urged him to flee Rome, but he didn't want to do this. And this is in character for a man whom St. Ambrose says went toward persecution instead of away from it.
So, instead, St. Sebastian went to an outdoor stairway, where the emperor would have to pass on his way to offer sacrifice to the gods. And when he came, he rebuked him for unjustly persecuting the Christians, who helped the empire by their prayers. And today, with the inauguration, this is a good day to help our country by our prayers. When Diocletian recovered from his surprise, he asked, "Are you Sebastian, whom not long ago we ordered to be killed with arrows?" He replied, "For this purpose, my Lord Jesus Christ has deigned to raise me up, that I may come to you and testify before all the people, that your persecution against the servants of Christ has broken out by an unjust judgment."
Then Diocletian had St. Sebastian taken to the hippodrome of the palace and whipped until he died. When night fell, his body was dumped in the main sewer of Rome, so that Christians would not find it and honor him as a martyr. But St. Sebastian appeared to a pious matron in a vision and told her where to find his body. So at night she recovered his holy body, which she took for burial to the catacombs where the relics of Saints Peter and Paul were buried. In fact, the relics of the holy apostles had been moved for safekeeping to the catacombs that are now known by the name of St. Sebastian.
From the third century, these catacombs on the Appian Way were known as the Memoria Apostolorum for this reason, the place where the Apostles were buried. The Apostles were remembered. Their location made them a convenient pilgrimage destination, and pilgrims doubtless also heard about St. Sebastian and the other martyrs who were buried near the two apostles. The oldest list of feasts of martyrs celebrated at Rome from the year 354 lists on January 20th St. Fabian in the catacombs of St. Callixtus and St. Sebastian in these other catacombs. The two locations are within walking distance, so that day there would have been a double celebration, first of St. Fabian, the martyred pope, and then of St. Sebastian, the martyred soldier. The two saints shared a single celebration until after Vatican II.
Now we have to choose one or the other, and so I've chosen St. Sebastian, the one who is better known. His name comes from a Greek adjective that means venerable or worthy of reverence, and he was indeed venerable. He was celebrated after his death. Devotion to him spread throughout the Christian world. By AD 400, his feast was being celebrated in Carthage, in Africa. In the Christian East, his feast was placed on December 18th. When Christianity was legalized and even got imperial support, a church was built over the catacombs. Even though the relics of St. Peter and Paul were taken to new basilicas closer to the center of Rome, the church built over the catacombs was dedicated to them, for they had been there for so long, and pilgrims were of course still coming there. But St. Sebastian became known as the third patron of Rome, and after the ninth century, the church was known by his name.
In that same century, his relics were divided. His head was taken to the church of the Four Crowned Martyrs in Rome, the Quattro Coronati, where he had helped these martyrs, whom he had supposedly encouraged to persevere. Some of his bones were taken to the Abbey of St. Médard de Soissons in France, and the remaining relics were taken to St. Peter's Basilica. But in 1218, they were returned to the church of St. Sebastian, built over the catacombs.
Over the centuries, St. Sebastian became known particularly as an intercessor against plagues. This probably began in the summer of 680, when a terrible epidemic broke out in Rome. They prayed to St. Sebastian, and the epidemic rapidly came to an end. Something similar happened in Pavia, and other once famous cases of St. Sebastian stopping epidemics occurred, or stopping the plague, occurred in Milan in 1575, and in Lisbon in 1599.
But what the Church hopes most that we will learn from St. Sebastian is his fortitude. We must obey God rather than men. When men tell us to do something sinful, it may cost us to obey God, but He will repay us abundantly, as He did this holy martyr.
Praised be Jesus and Mary, now and forever.