Following their victory, the Maccabees, sons of the Priestly Hasmonean family which led the Jews in their revolt against the Syrian overlords, entered the Holy Temple in Jerusalem defiled by the Syrian invaders, cleansed it and dedicated it anew to the service of God. Then, in memory of their victory, the Maccabees celebrated the first Hanukkah. (Hanukkah is the Hebrew term for dedication).
The Talmud, the body of Jewish oral law, relates how the Judean heroes,
led by Judah Maccabee, were making ready to rededicate the Temple
and were unable to find enough undefiled oil to light the lamps.
However, in one of the Temple chambers, they finally came upon a
small cruse of oil which,
under normal circumstances,
would have lasted only one evening. Miraculously, this small amount
of oil kept the Temple lights burning, not for one night, but for
all the eight nights until new oil fit for use in the
temple could be obtained. This is the miracle commemorated by the
kindling of the Hanukkah lights.