Its origins go back to the ancient Roman celebration of Lupercalia, which honored the gods Lupercus and Faunus, and the legendary founders of Rome, Romulus and Remus. Lupercalia festivities and feasts are purported to have included the pairing of young women and men. Men would draw women's names from a container and each couple would be paired until next year's celebration.
It was not called "Valentine's Day" until a priest named Valentine came along. Emperor Claudius handed down a decree that soldiers remain single, believing that soldiers would be distracted and unable to concentrate on fighting if they were married or engaged. Valentine converted many guards to Christianity and defied the emperor by secretly performing marriage ceremonies. As a result of his defiance, Valentine was put to death on February 14. As Christianity spread through Rome, priests moved Lupercalia from February 15 to February 14 and renamed it St. Valentine's Day.
Cupid became associated with Valentine's day for another reason. According to Roman mythology, Cupid was the son of Venus, the goddess of love and beauty. He caused people to fall in love by shooting them with his magical arrows. He also fell deeply in love with a mortal maiden named Psyche. Cupid married Psyche, but his mother, Venus was jealous of Psyche's beauty and forbade her daughter-in-law to look at Cupid. Psyche couldn't resist temptation and sneaked a peek at her handsome husband. As punishment, Venus demanded that she perform three tasks, the last of which caused Psyche's death. Cupid brought Psyche back to life and the gods, moved by their love, granted Psyche immortality.