Olympia

Olympia was a rugged and mountainous world, most of the world's population being centred in giant city states. The plentiful quantities of quarried stone and the mountainous terrain of the planet made siege warfare the only way to maintain military security, hence producing Perturabo's adeptness with siege warfare in his command of the Iron Warriors.

During the cleansing of Gugann, the people of Olympia broke out in open revolt. It was Horus, Warmaster of the Emperor, that brought this to his attention. Through Horus' gift of the hammer Forgebreaker an unspoken pact was signed between the two and Perturabo left with his Iron Warriors to quell this rebellion.

Moving from one city state to the next, the rebellion was stopped, the Iron Warriors sparing no one as they had become accustomed to giving o quarter to their enemies. Nothing was left of the cities but smoldering pyres, 5 million civilians dead.

After having taken part in the Horus Heresy, the Iron Warriors retreated into the Eye of Terror with the other Traitor Legions and took a world for themselves called Medrengard. Nothing is known for certain what the world truly looks like, as the realm of Chaos is constantly shifting, but the report of Inquisitor Maul describes it as a world that is one great fortress, the entire world transformed into a tremendous fortified position with impossibly high towers and Chaos warships hovering everywhere above it.