Valentine's Day also know as Saint Valentine's Day or the Feast of Saint Valentine is celebrated in many countries around the world, although it is not a holiday in most of them.
It is thought to be named after a Christian martyr dating back to the 5th century, but has origins in the Roman holiday Lupercalia.
A popular account of Saint Valentine of Rome states that he was imprisoned for performing weddings for soldiers who were forbidden to marry because it was considered that bachelors made better soldiers, and for ministering to Christians, who were persecuted under the Roman Empire.
Saint Valentine supposedly wore a purple amethyst ring, customarily worn on the hands of Christian bishops with an image of Cupid engraved in it, a recognizable symbol associated with love that was legal under the Roman Empire; Roman soldiers would recognize the ring and ask him to perform marriage for them. Probably because of the association with Saint Valentine, amethyst has become the birthstone of February.
During his imprisonment it is thought that he healed the daughter of his jailer, Asterius.and before his execution he wrote her a letter signed "Your Valentine" as a farewell.
In 1381 it was Geoffrey Chaucer, the English poet who first linked St. Valentine's Day with romance.
Chaucer composed a poem in honour of the royal engagement between England's Richard II and Anne of Bohemia. He marked the occasion with an association between a feast day, the mating season of birds (which takes place in February in England) , and St. Valentine's Day in the poem "The Parliament of Fowls," circa 1381.
“For this was on seynt Volantynys day Whan euery bryd comyth there to chese his make.”
(“For this was on St. Valentine's Day, When every fowl cometh there to choose his mate.”) In 18th-century England, it evolved into an occasion in which lovers and admirers expressed their love for each other by presenting flowers, offering sweets, and sending hand made cards of lace, ribbons, and featuring hearts, and cupids (known as "valentines").
With little exception, hand made cards have for the best part given way to mass produced cards but still remain a gesture of love.
How Do I Love Thee?
How Do I Love Thee? Let me count the ways.
I love thee to the depth and breadth and height
My soul can reach, when feeling out of sight
For the ends of Being an ideal Grace.
I love thee to the level of everyday's
Most quiet need, by sun and candlelight.
I love thee freely, as men strive for Right;
I love thee purely, as they turn from Praise.
I love thee with the passion put to use
In my old griefs, and with my childhood's faith.
I love thee with a love I seemed to lose
With my lost saints,- I love thee with the Breath,
Smiles, tears, of all my life!- and, if God choose,
I shall but love thee better after death.
- Elizabeth Barret BrowningLove Sonnet 18
Shall I compare thee to a summer's day?
Thou art more lovely and more temperate:
Rough winds do shake the darling buds of May,
And summer's lease hath all too short a date:
Sometime too hot the eye of heaven shines,
And often is his gold complexion dimm'd;
And every fair from fair sometime declines,
By chance or nature's changing course untrimm'd;
But thy eternal summer shall not fade
Nor lose possession of that fair thou owest;
Nor shall Death brag thou wander'st in his shade,
When in eternal lines to time thou growest:
So long as men can breathe or eyes can see,
So long lives this and this gives life to thee.
- William ShakespeareTo His Valentine 
Must, bid the morn awake,
Sad winter now declines,
Each bird doth choose a mate,
This day's St. Valentine's;
For that good bishop's sake
Get up, and let us see,
What beauty it shall be,
That fortune us assigns.
But lo, in happy hour,
The place wherein she lies,
In yonder climbing tow'r,
Gilt by the glittering rise;
O Jove! that in a show'r,
As once that thund'rer did,
When he in drops lay hid,
That I could her surprise.
Her canopy I'll draw,
With spangled plumes bedight,
No mortal ever saw
So ravishing a sight;
That it the gods might awe, A
nd pow'rfully transpierce
The globy universe,
Out-shooting ev'ry light.
My lips I'll softly lay
Upon her heav'nly cheek,
Dy'd like the dawning day,
As polish'd ivory sleek;
And in her ear I'll say,
"O thou bright morning-star,
'Tis I that come so far,
My valentine to seek.
"Each little bird, this tide,
Doth choose her loved pheer,
Which constantly abide
In wedlock all the year,
As nature is their guide:
So may we two be true,
This year, nor change for new,
As turtles coupled were. —
"Let's laugh at them that choose
Their valentines by lot.
To wear their names that use,
Whom idly they have got;
Such poor choice we refuse,
Saint Valentine befriend;
We thus this morn may spend,
Else, Muse, awake her not."
- Michael DraytonSongHow many Times do I love thee, dear?
Tell me how many thoughts there be
In the atmosphere
Of a new-fall’n year,
Whose white and sable hours appear
The latest flake of Eternity:
So many times do I love thee, dear.
How many times do I love again?
Tell me how many beads there are
In a silver chain
Of evening rain,
Unravell'd from the tumbling main,
And threading the eye of a yellow star: -
So many times do I love again.
- Thomas Lovell Beddoes I Love Thee
I love thee -- I love thee!
'Tis all that I can say; --
It is my vision in the night,
My dreaming in the day;
The very echo of my heart,
The blessing when I pray:
I love thee -- I love thee!
Is all that I can say.
I love thee -- I love thee!
Is ever on my tongue;
In all my proudest poesy
That chorus still is sung;
It is the verdict of my eyes,
Amidst the gay and young:
I love thee -- I love thee!
A thousand maids among.
I love thee -- I love thee!
Thy bright and hazel glance,
The mellow lute upon those lips,
Whose tender tones entrance:
But most, dear heart of hearts, thy proofs
That still these words enhance,
I love thee -- I love thee!
Whatever be thy chance.
- Thomas Hood 
Because of the romantic nature of the day, Valentines Day is often chosen as the time for marriage proposal with the man getting down on one knee and offering his hand in marriage. This gesture represents the chivalry of courtly love acted out by nobles in the royal courts during the high middle ages.
