The good Saint Valentine was a priest at Rome in the days of Claudius II.  He and Saint Marius aided the Christian martyrs, and for this kind deed Saint Valentine was apprehended and dragged before the Prefect of Rome, who condemned him to be beaten to death with clubs and to have his head cut off.  He suffered martyrdom on the 14th day of February, about the year 270.
 
At that time it was the custom in Rome, a very ancient custom, indeed, to celebrate in the month of February the Lupercalia, feasts in honor of a heathen god.
 
On these occasions, amidst a variety of pagan ceremonies, the names of young women were placed in a box, from which they were drawn by the men as chance directed.
 
The pastors of the early Christian Church in Rome endeavored to do away with the pagan element in these feasts by substituting the names of saints for those of maidens.  And as the Lupercalia began about the middle of February, the pastors appear to have chosen Saint Valentine's Day for the celebration of this new feast.
 
So it seems that the custom of young men choosing maidens for valentines, or saints as patrons for the coming year, arose in this wise.