There are different versions of his story, but one likely goes like this:
It was 269 A.D.
The Roman governor Claudius was seeking a way to strengthen his army. He pontificates that soldiers who have wives at home may not fight as bravely on the front lines for fear that they will not return home to their family. Therefore, he made marriage illegal for soldiers. He believed that loyalty to the state would supersede the natural desire to marry, birthing a generation of soldiers completely loyal to Rome.
He was wrong, of course. Many soldiers desired to marry in spite of his decree.
A young priest named Valentine held the firm conviction that marriage should not be denied by the state. He began to secretly and illegally perform marriage ceremonies. More and more Roman soldiers sought him out.
Valentine's crime was eventually uncovered. He was brought before Claudius and told to repent. He refused, believing that he must be faithful to his new King, whom he claimed to be a resurrected Jewish rabbi named Jesus, over the King of Rome. He was immediately arrested and condemned to die as a traitor. From his prison cell, Valentine wrote notes of encouragement to his family and friends signed "from your Valentine."
On February 14th, 270 he was executed.
But not before making a mark on history for standing on the side of love.
And that is (possibly) the real story behind why florists and chocolatiers are having such a good day today.