2 Answers

The ancient Roman festival that some say started valentine's day and was called Saturnalia. At the Roman festival which happened on the 15th of February in which boys would draw girls names out of a hat and get her for a period of time.

http://wiki.answers.com/Q/What_roman_festival_is_associated_with_valentines_day

Saturnalia was first held in Rome around 200 b.c. after the Carthaginians defeated the Romans in battle, and it was held in December. The god being appeased was Saturn or Cronus, the god attributed with control over time. The Saturnalia originally included an animal sacrifice. Romans would dress in more elaborate clothing, and slaves were allowed for this period of time to treat their masters with pretend disdain. It is only after much more time that Saturnalia morphed into something somewhat similar to Valentine's day, and the reason for the correlation has to do with what Vampira mentions above.