Gaia was really angry that
Zeus had punished some of her children really hard after the victory against the titans,
so she gave birth to some really ugly creatures. They had snakes
instead of hairs and their bodies ended in a dragon tail: the
Giants.
The first work these creatures had was to head to the Olympus, the house
of the gods, to destroy
everything.
Though
even if the giants were descendants of the gods, they were not immortal.
However, the Moiré had already foretold that for their
victory the gods would need the help of a mortal. Gaia
planted a herb that should make the giants immortal,
but fortunately Zeus discovered it before they could use it and he destroyed the herb.
The
mortal help came in the form of Heracles, who supported the gods
in their fight against the giants. This was somehow the last hard exam
for the gods, who managed to stand a second hard battle about the ruler
ship of the earth even after the battle with the titans.

The Beginning / Gods of the Olympus / Smaller Gods