The holiday of Valentine's Day probably derives its origins from the ancient Roman feast of Lupercalia. In the early days of Rome, fierce wolves roamed the woods nearby.  The people entreated the god Lupercus, protector of the herd and crops, to protect their flocks and keep animals and people healthy and fertile through singing and dancing. A festival held in honor of Lupercus was celebrated February 15th. The festival was celebrated as a spring festival. Their calendar was different at that time, with February falling in early springtime.
One of the customs of the young people was name-drawing. On the eve of the festival of Lupercalia, the names of Roman girls were written on slips of paper and placed into a ceramic jar. Each young man drew a girl's name. They would be partners in the festivities and dances, oft times they would not need to participate in this particular event the next year.
Legend has it that the holiday became Valentine's Day after a priest named Valentine. Valentine was a priest in Rome at the time Christianity was a new religion. The Emperor at that time, Claudius II, ordered the Roman soldiers NOT to marry because Claudius believed that if they did, they would rather stay home with their families than fight his wars. Valentine defied the Emperor's decree and secretly married the young couples. He was eventually arrested, imprisoned, and put to death.
Valentine was beheaded on February 14th, the eve of the Roman holiday Lupercalia. As Rome became more Christian, the priests moved the festival to the 14th to honor St. Valentine instead of Lupercus.  Over time, the combined themes of fertility, love and romance have endured and evolved into our contemporary celebrations, where friends and lovers exchange love notes (valentines) and romantic gifts for Valentines.