Otus and Ephialtes

Mt. Ossa

In Metamorphoses 12, Ovid sets the battle of the Lapiths and Centaurs in Thessaly near Mounts Pelion (named for Achilles' father, Peleus) and Ossa. As is often the case, the setting is resonant with stories. One relevant here is the tale of Otus and Ephialtes, two giant fellows who decided one day to go after Artemis and Hera (not unlike Ixion). They were known as the Aloadae. According to the story:

Parada

Ephialtes 2 and Otus 1, two giants called the ALOADS tried to unseat Zeus from his throne. The ALOADS grew every year a cubit in breadth and a fathom in height; and when they were nine years old, being nine cubits broad and nine fathoms high, they resolved to fight against the gods. They then set Ossa on Olympus, and having set Pelion on Ossa they threatened by means of these mountains to ascend up to heaven. 

They also declared that by filling up the sea with the mountains they would make it dry land, and the land they would make sea. Ephialtes 2 wooed Hera, and Otus 1 wooed Artemis; and they put Ares in bonds. But when they wished to assault Artemis and she could not resist their strength, Apollo sent a deer between them. So driven mad by anger in trying to kill it with javelins, they killed each other. 

But others assert that Artemis caused their death; that she changed herself into a deer and leaped between them, and in their eagerness to hit the quarry they threw their darts at each other. In the Underworld they are punished thus: they are bound by serpents to a column, back to back. Between them is a screech-owl, sitting on the column to which they are bound.

Wikipedia 

In Greek mythology, the Aloadae (or Aloadai; Ancient Greek: Ἀλωάδαι) were Otus (Ὦτος) and Ephialtes (Ἐφιάλτης), sons of Iphimedia, wife of Aloeus, by Poseidon,[1] whom she induced to make her pregnant by going to the seashore and disporting herself in the surf or scooping seawater into her bosom.[2] From Aloeus they received their patronymic, the Aloadai. They were strong and aggressive giants, growing by nine fingers every month[3] nine fathoms tall at age nine, and only outshone in beauty by Orion.[4][5] 

The brothers wanted to storm Mt. Olympus and gain Artemis for Otus and Hera for Ephialtes. Their plan, or construction, of a pile of mountains atop which they would confront the gods is described differently according to the author (including Homer, Vergil, and Ovid), and occasionally changed by translators. Mount Olympus is usually said to be on the bottom mountain, with Mounts Ossa and Pelion upon Ossa as second and third, either respectively or vice versa. 

A few more Parthenon images of the battle of Lapiths and Centaurs are in this album of photos from a visit we made to the British Museum a few years ago.