While some believe that Valentine's Day is celebrated in the middle of February to commemorate the anniversary of Valentine's death or burial—which probably occurred around A.D. 270--others claim that the Christian church may have decided to place St. Valentine's feast day in the middle of February in an effort to “Christianize” the pagan celebration of Lupercalia.
Celebrated at the ides of February, or February 15, Lupercalia was a fertility festival dedicated to Faunus, the Roman god of agriculture, as well as to the Roman founders Romulus and Remus.
Valentine's Day began to be popularly celebrated around the 17th century. By the middle of the 18th, it was common for friends and lovers of all social classes to exchange small tokens of affection or handwritten notes, and by 1900 printed cards began to replace written letters due to improvements in printing technology.
Today, according to the Greeting Cards Association, an estimated 1 billion Valentine's Day cards are sent each year, making Valentine's Day the second largest card-sending holiday of the year.
Thus the LOVE DAY is one of the most celebrated day around the globe. Love is an undefinable feeling , where someone becomes world to you, and just care love and concern exist, that person stays on to your mind 24x7 and his /her interest and happiness comes first to you than yours.