Zeus and three Gigantes, drawing based on the Zeus Pergamon Altar
Another less violent version is that Giants were produced by Gaia.
The Gigantes later attacked the gods of Mt. Olympus, trying to reach them by stacking the two mountain ranges of Thessaly, Pelion and Ossa, on top of each other. With the help of Heracles though, the Gigantes were defeated.
Enceladus, one of the Gigantes, was placed beneath Mt. Etna. The rumbling of the volcano was caused by him rolling around. Athos, another one of the Gigantes, threw a mountain at Zeus, who knocked it to the ground near Macedonia. This mountain was the holy peak of Mount Athos.
Gigantomachy from the Siphnian Treasury in Delphi, North Frieze, 530-525 BC, Delphi Archaeological Museum. On the left side Apollo and his sister Artemis against the giants. One giant tries to escape (his name from what we can read is Tharos or Ka[n]tharos). Ephialtes lies dead on the ground. A group of three other giants on the right side (Hyperphas, Alektos and one whose name is lost). The proud artist of this work wrote his name on the shield of the last of the three giants but it was lost
Giants, size comparison of different types 1678, A. Kircher