Here is what we read in the 1961 edition of the Roman Martyrology for today:
At Rome, on the Via Flaminia, the birthday of St. Valentine, Priest and Martyr, who, after many wondrous works of healing and teaching, was scourged with rods and beheaded under Claudius Caesar.
At Terni, St. Valentine, Bishop and Martyr, who, after lengthy ill-treatment was imprisoned; and since he could not be overcome, he was brought out of his prison in the silence of midnight and beheaded, at the command of Placidus, prefect of the city.
-- The Roman Martyrology, February 14th
We read this in the Catholic Encyclopedia:
At least three different Saint Valentines, all of them martyrs, are mentioned in the early martyrologies under date of 14 February. One is described as a priest at Rome, another as bishop of Interamna (modern Terni), and these two seem both to have suffered in the second half of the third century and to have been buried on the Flaminian Way, but at different distances from the city. In William of Malmesbury's time what was known to the ancients as the Flaminian Gate of Rome and is now the Porta del Popolo, was called the Gate of St. Valentine. The name seems to have been taken from a small church dedicated to the saint which was in the immediate neighborhood. Of both these St. Valentines some sort of Acta are preserved but they are of relatively late date and of no historical value. Of the third Saint Valentine, who suffered in Africa with a number of companions, nothing further is known.
Saint Valentine's Day
The popular customs associated with Saint Valentine's Day undoubtedly had their origin in a conventional belief generally received in England and France during the Middle Ages, that on 14 February, i.e. half way through the second month of the year, the birds began to pair. Thus in Chaucer's Parliament of Foules we read:
"For this was sent on Seynt Valentyne's day
Whan every foul cometh ther to choose his mate."
For this reason the day was looked upon as specially consecrated to lovers and as a proper occasion for writing love letters and sending lovers' tokens...
While St. Valentine is no longer found within the general liturgical calendar that is used within the modern Roman liturgy (it is still found in the liturgical calendar of the usus antiquior of course), it is worth noting that the recent 2004 edition of the Martyrlogium Romanum still lists a St. Valentine, martyr, for this day: "Romae via Flaminia iuxta pontem Milvium, sancti Valentini, martyris."
In the Byzantine East, Saint Valentine, priest and martyr, is commemorated on July 6th, and Saint Valentine, bishop and martyr, on July 30th.
Relics of St. Valentine in the church of Santa Maria in Cosmedin, Rome, decorated for February 14th
(Photo by Br. Lawrence Lew, O.P.)