It may not be fair to say that Valentine's Day has its origin in antiquity, but there were romantic spring holidays (Gamelion and Lupercalia) and a St. Valentine or two.
GamelionGreek months don't line up nicely with the modern calendar. They tend to run from midway through one month to midway through the next. So mid-January to mid-February was the Athenian month called Gamelion or the "Month of Marriage." A sacred marriage (hieros = holy, sacred + gamos = marriage) was celebrated at the end of the month of Gamelion to mark the marriage of the king and queen of the gods, Zeus and Hera. Preparation for this festive event included purification.
FebruariusIn Rome Februarius 'February' was also a month for purification, but in Rome, it was to prepare for the new year, which began in March. The 2 annually elected consuls took office on the Ides of March (March 15). If the calendar needed adjustment, priests stuck in extra days before the Kalends (1st) of March. Houses were swept, and sprinkled with salt and spelt.
February, Purification, and the LupercaliaThe word Februarius comes from a word meaning purification or purgation.
Twin themes of purification and fertility come together in the Roman February holiday called Lupercalia.
Priests (luperci) came from 2 colleges, the Quintilii and Fabii. These are also the names of old Roman patrician gentes, and members of the luperci were, at least originally, members of these patrician gentes. Although gradually, plebeians gained power, some of the priestly offices remained in the hands of the patricians throughout the regal and republican periods of Rome.
The luperci met at the cave where the she-wolf supposedly nursed the foundling twins Romulus and Remus. Vestal Virgins offered their special, holy salt-cakes, called mola salsa. Priests sacrificed a dog and a goat, and smeared the animal blood on 2 boys who, clad only in a bit of goatskin, led a band of revelers. The antics of the boys included whipping bystanders with a goatskin strip (called a februa). Women so whipped -- even previously barren ones -- were thought to become fertile.
The priests may also have paired up young men and women who were to stay paired up for the remainder of the year.
Mark Antony was the first magister (master) of the luperci from a third college, the Julii, which was created during the time of Julius Caesar.
Shakespeare mentions the Lupercalia in his Julius Caesar:
See whether their basest metal be not moved;
They vanish tongue-tied in their guiltiness.
Go you down that way towards the Capitol;
This way will I disrobe the images,
If you do find them deck'd with ceremonies.
May we do so?
You know it is the feast of Lupercal.
Julius Caesar Act 1, Scene 1.