In the early martyrologies, three different St. Valentines are mentioned, all sharing Feb. 14 for a feast day. The 1st -
A Roman Priest during the reign of Emperor Claudias II who persecuted the church at that particular time," an edict prohibited the marriage of young people. This was based on the hypothesis that unmarried soldiers fought better than married soldiers because married soldiers might be afraid of what might happen to them or their wives or families if they died."Valentine was caught, imprisoned and tortured for performing marriage ceremonies against command of Emperor Claudius II.
Emperor Claudius came to like Valentine, too, so he offered to pardon Valentine and set him free if Valentine would renounce his Christian faith and agree to worship the Roman gods. Not only did Valentine refuse to leave his faith, he also encouraged Emperor Claudius to place his trust in Christ. Valentine’s faithful choices cost him his life. Emperor Claudius was so enraged at Valentine’s response that he sentenced Valentine to die. Valentine prayed with and healed Julia, and Asterius himself became Christian as a result.
Valentine used his time in jail to continue to reach out to people with the love that he said Jesus Christ gave him for others.
Before he was killed, Valentine wrote a last note to encourage Julia to stay close to Jesus and to thank her for being his friend. He signed the note: “From your Valentine.” That note inspired people to begin writing their own loving messages to people on Valentine’s Feast Day.
In the year 269 AD, Valentine was sentenced to a three part execution of a beating, stoning, and finally decapitation all because of his stand for Christian marriage. The story goes that the last words he wrote were in a note to Asterius' daughter. He inspired today's romantic missives by signing it, "from your Valentine." Eventually, St. Valentine was also arrested, condemned to death for his faith, beaten with clubs, and finally beheaded on Feb. 14, AD 270. He was buried on the Flaminian Way. Later, Pope Julius I (333-356) built a basilica at the site which preserved St. Valentine's tomb. Archeological digs in the 1500s and 1800s have found evidence of the tomb of St. Valentine. However, in the thirteenth century, his relics were transferred to the Church of Saint Praxedes near the Basilica of St. Mary Major, where they remain today. Also, a small church was built near the Flaminian Gate of Rome which is now known as the Porta del Popolo but was called in the 12th century "the Gate of St. Valentine," as noted by the early British historian William Somerset (also known as William of Malmesbury, d. 1143), who ranks after St. Bede in authority.
SOURCE: Edited with info from Catholic Enclopedia - Updated Feb 14