Exactly three years after the Temple was defiled, Judah Maccabee and his followers reclaimed, cleaned, and rededicated it. When they were ready to light the menorah that was always to be kept burning, however, they could find only one small flask of oil -- enough for a day. According to legend, that oil burned for eight days, the amount of time they needed to get more.
To commemorate this miracle, Jews everywhere celebrate Hanukkah (Hebrew for "dedication") by lighting menorah candles for eight nights. The celebration begins on the 25th of Kislev.