Why was Saint Valentine sentenced to death?

The legend says that Roman Emperor Claudius II Gothicus needed to raise an army but could not draft married men. He made it against the law for people to marry. Valentine continued to marry couples in secret until the authorities caught up with him. He was arrested, tortured and beheaded.

There is no doubt that at least one Saint Valentine existed, in fact, there are about 14 recognized by the Church. Confusion arises because two of these Valentines suffered martyrdom in Rome about the same time under Roman Emperor Claudius II Gothicus. One was a priest working in Rome and the second was Valentine the Bishop of Interamna, Terni, in Italy, who happened to be in Rome on Church business at the time. Their lives had become so intertwined and embellished by hagiographers over the years that it became impossible to separate them and the stories circulating. What was truth and what was legend? In 1969, due to this confusion, Saint Valentine was removed from the Calendar of Saints. His cult has not been suppressed so veneration is still allowed. However, any saint undergoing martyrdom for their faith is most worthy of veneration even if the whole story remains shrouded in mystery and legend.