Valentine defied this decree and urged young lovers to come to him in secret so that he could join them in the sacrament of matrimony. Eventually he was discovered by the Emperor, who promptly had Valentine arrested and brought before him. Because he was so impressed with the young priest, Claudius attempted to convert him to Roman paganism rather than execute him. However, Valentine held steadfast and in turn attempted to convert Claudius to Christianity, at which point the Emperor condemned him to death.
While in prison, Valentine was tended by the jailer, Asterius, and his blind daughter. Asterius' daughter was very kind to Valentine and brought him food and messages. They developed a friendship and toward the end of his imprisonment Valentine was able to convert both father and daughter to Christianity. Legend has it that he also miraculously restored the sight of the jailer's daughter.
The night before his execution, the priest wrote a farewell message to the girl and signed it affectionately "From Your Valentine," a phrase that lives on even to today. He was executed on February 14th, 273 AD in Rome. The Martyrology says, "At Rome, on the Flaminian Way, the heavenly birthday of the blessed martyr Valentine, a priest. After performing many miraculous cures and giving much wise counsel he was beaten and beheaded under Claudius Caesar."
The church in which he is buried existed already in the fourth century and was the first sanctuary Roman pilgrims visited upon entering the Eternal City.
The valentine has become the universal symbol of friendship and affection shared each anniversary of the priest's execution -- St. Valentine's Day. Valentine has also become the patron of engaged couples.
[From CatholicCulture.org]
Almighty God, by whose grace and power thy Martyr Valentine was enabled to witness to the truth and to be faithful unto death: grant that we, who now remember him before thee, may likewise so bear witness unto thee in this world; that we may receive with him the crown of glory that fadeth not away; through Jesus Christ thy Son our Lord, who liveth and reigneth with thee, in the unity of the Holy Spirit, ever one God, world without end. Amen.