Olympia is the now dead world where the pod of the Primarch Perturabo of the Iron Warriors landed. Before it became the barren dead world it is today, Olympia was once a mountainous planet where the population resided in large city states throughout the planet. One of the cities was called Lochos where Pert's adoptive father resided.
Before the coming of Perturabo and the Emperor, Olympia was dominated by several warlords who ruled over the city-states around the desolate planet. Olympia had been intensively strip mined during the Dark Age of Technology, so now practically no fissile or precious conductive materials were left under the crust, that meant that even if the population had the necessary know-how to build advanced technology, they simply couldn't thanks to the lack of resources. So it had devolved to a Steampunk society of airships, swords and moustache-twirling courtly intrigue.
After Perturabo smashed into the mountains after being flung from the Emperor's laboratory, he apparently wandered around for a bit, slaying monsters and generally being a cool guy, but for some unknown reason Perturabo himself had no memory of any of it. His first recollection was climbing a cliff face to be met by some soldiers who wanted to take him to their king, where he was adopted by the powerful warlord Dammekos. Pert was a pretty emo kid, not showing any love for anyone despite his father the Tyrant of Lochos spending a lot of time with him, although that quality "father-son" time mostly revolved around Dammekos parading Perturabo in front of the Tyrant-Lords of other cities, showing off how clever the boy was, how skilled he was, and using him to beat up the champions of the other Tyrants to get their allegiance.
Perturabo, having little else to do on a planet with no resources, eventually claimed the world for his father and had to wait around until something changed.
Destruction of Olympia
That went relatively well until his old-father was killed and the population decided to rise up in rebellion against the Imperium. At hearing his old home had turned its back on their allegiance to the Emperor, Perturabo flew into an apocalyptic rage, quit his current campaign against the Hrud and sent his entire fleet back to Olympia, pushing so hard that one of his cruisers detonated the moment it translated in-system. He then decided he was going to make an example.
He ordered his Iron Warriors to build him a vantage point on a mountain over one of the chief cities and then extend a parlay to every political leader on the planet. When all the nobles arrived at the agreed time and place, Perturabo sat silently for a bit and let them try to negotiate with him, allowing them to get more and more wound up at his lack of engagement. When they started pissing him off he shouted them all down and ordered the city they were overlooking destroyed from orbit. This was no negotiation but a lesson. They had betrayed the Emperor, but he was willing to give them a choice: Just like when he took control of his Legion, he would enact decimation on the population, allowing the civilians to brutally murder 10% of themselves so the rest might be saved. Otherwise fucking EVERYONE would get massacred by the fucking Adeptus Astartes and all the cool siege weapons the Iron Warriors loved so much. Suffice to say the planetary leaders thought this was utter madness and rejected his offer, so Perturabo had them all gunned down on the spot and went to war with the planet. The eventual result was predictable: Extermination of the entirety of Olympia's standing armies, enslavement of the populace and taking of every suitable child for Astartes implantation.
The war broke the Legion as many Iron Warriors refused to shoot innocent civilians, but Perturabo was in such an unforgiving mood that he ordered them to be dealt with the same way. Afterward, Perturabo realised what he had done and silently broke down, having to be discreetly removed from the planet by Thunderhawk in case anyone saw him like that. He rescinded his orders and allowed anyone who was not already killed or enslaved to be left alone so that they might salvage the pieces. Perturabo understood that he had crossed a line that he could never turn back from, claiming he had become just like his brother Konrad Curze.
Horus then swayed Perty from the Emperor's light, saying that killing your own people in the millions was a-okay and that the idiots deserved it. Might makes after all right!
During the end of the Horus Heresy, the Iron Warriors decided to set up camp back on Olympia for two years whilst the Smurfs and Imperial Fists attacked them. The Iron Warriors then had to evacuate as all the missile reserves and other cool exploding things exploded, turning Olympia into a barren wasteland. It was then declared Perdita(Latin for lost). The Iron Warriors evacuated to Medrengard, a daemon world in the Eye of Terror, and established it as their new homeworld.
The original fluff states that it was Horus who informed Perturabo that the planet had rebelled, and had been pushing him to the breaking point by sending the Perturabo and his legion into harder and harder battles in order to get the Iron Warriors on side.
The Forgeworld books corroborate this somewhat, by stating that the razing of Olympia took place in 004.M31, which was the same year Horus fell at Davin. But even though Perturabo and his legion were already tired of years of endlessly throwing themselves into difficult battles it doesn't provide a lot of time for a traitorous Horus to mentally break down his brother with long term abuse.
The Black Library series puts the destruction of Olympia at 000-001.M31. This places the event several years prior to Horus turning to Chaos, but the same year that Horus gets named Warmaster. This puts a whole different spin on things, showing that Perturabo broke all on his own without being influenced by the traitors due to his legion fighting wars at the Emperor's insistence rather than Horus.
These can possibly reconciled by suggesting that the first person accounts given in the Black Library books are true, but the since the Forgeworld books and original 90s Index Astartes articles were written both after-the-fact and from an Imperial point of view; getting the date wrong (whether by accident or design) conveniently puts the blame for Perturabo's fall on Horus, rather than the Emperor.
|The Planets, Systems, Regions and Sectors of the Galaxy|
|Imperial Homeworlds:||Holy Terra - Sacred Mars|
|Primarch Homeworlds:||Baal - Barbarus - Caliban - Chemos - Chogoris - Colchis |
Cthonia - Deliverance - Fenris - Inwit - Medusa - Nostramo
Nocturne - Nuceria - Olympia - Prospero - Macragge
|Notable Imperial Worlds:||Armageddon - Bakka - Cadia - Catachan - Cretacia - Ganymede |
Hydraphur - Necromunda - Phyrr - Pythos - Krieg - Kronus - Sacris
Sanctuary 101 - Scelus - Scintilla - Tanith - Tartarus - Titan - Vigilus
Vraks - Zayth - 108/Beta-Kalapus-9.2
|Daemon Worlds:||Plague Planet - Sortiarius - Sicarus - Medrengard - Glass Moon |
Fleshworld - Bathamor - Black Marble
|Systems and Regions:||Ghoul Stars - Halo Zone - Jericho Reach - Kaurava System |
Solar System - Stygius Sector - T'au Septs - Taelus System - Ultramar
|Types of Worlds:||Agri-World - Craftworld - Daemon World - Death World - Eldar World |
Forge World - Fortress World - Hive World - Civilised World - Tomb World