Prospero was the original homeworld of the Thousand Sons Traitor Legion of Chaos Space Marines and their Primarch Magnus the Red. It was a center of knowledge and lore, particularly knowledge of sorcery and the Warp before its surface and its planetary capital of Tizca were scoured by the planetary assault of the Space Wolves Space Marine Legion at the start of the Horus Heresy in the early 31st Millennium. This assault was arranged by the Warmaster Horus, who sought to turn the Astartes Legions against one another and to drive the Thousand Sons into the arms of Chaos so that they would support his own attempt to overthrow the Emperor of Mankind. After the Space Wolves' assault, Prospero was declared a Dead World by the Imperium, like all of the former homeworlds of the Traitor Legions.
Chosen by its settlers for the planet's isolated position although it still remained far closer to Terra than many other human colonies settled during the Dark Age of Technology, the Civilised World of Prospero had only a few redeeming qualities. It possessed no independent resources, little contact with any outsiders and only a few sources of nourishment. The only reason for planting a colony there was because it was a very good place to hide, and thus became a large community of psychically talented and often physically mutated humans who could find no refuge elsewhere in the galaxy.
During the Great Crusade, Prospero had developed into a paradise world. Many of the vast buildings on the planet were massive gold and marble pyramids. Prospero was a planet with blue skies and gleaming Egyptianesque architecture. One of the world's many cities was the capital city of Tizca, often referred to as the City of Light, where the Thousand Sons later held out against the Space Wolves when they were mistakenly declared traitors against the Imperium.
Prospero's "cleansing" at the hands of the Space Wolves was hastened by the dilapidated state of the planetary defenses. As the homeworld of a Space Marine Legion, it was standard for the surface of such a planet to be protected by immense planetary Defence Lasers sunk into reinforced silos many miles beneath its settlements. Orbital fire platforms, automated tracking stations, minefields, as well as a number of the Legion's own starships -- all were manned continuously and diligently.
Even if no overt attempts were made to reinforce the garrison of Prospero, save for the recalling of much of the XV Legion to its homeworld, it remained a mighty fortress. The majority of that then-verdant globe was covered in broken hills and dense forests, its ancient cities little but time-scoured ruins with only heavily fortified Legion outposts, small migratory settlements and the largely subterranean enclave belonging to the Zhao-Arkhad Forge World of the Mechanicum to be found outside of the capital city of Tizca. Yet this was no weakness in the world's defences, for the wilderness that was Prospero, though lush in appearance, was known to be infested with a sickening variety of xeno-fauna, the most infamous being the deadly pseudo-insectile Psychneuein parasites, beings whose life-cycle extended into the fabric of the Empyrean, making them all but impossible to bar or exterminate. The hidden predatory swarms of these strange creatures would have made any attempt to achieve landfall in the wilds impractical, even for such a host as that gathered by Leman Russ and Constantin Valdor, leaving them no secure foundation from which to make a more conventional siege of Tizca from without.
In addition to to the harsh terrain and deadly fauna of Prospero, Tizca itself, the renowned "City of Light," presented yet another formidable obstacle to any attacker, geographically bounded as it was on all sides. To the north rose the sheer peaks of the White Mountains, studded with enclosed Defence Laser emplacements and fortified bunkers manned by the soldiers of the Prosperine Guard, and to the west lay the Valperine Sea, whose deep turquoise waters served to ward off conventional landings by sea. The focus of the Thousand Sons had always been set on other goals besides the traditional Space Marine role of combat, particularly the acquisition of knowledge concerning sorcery and psychic abilities. This distraction had led to a dangerous weakening of the Prosperine defence grid. The cavernous subterranean Defence Lasers had been neglected, left unmanned and poorly maintained, while the orbital defences were virtually non-existent. As a result, the arrival of the Imperial Censure Host armada went uncontested, their orbit-to-surface ordnance barrages unanswered and their Drop Pods unchallenged.
Ironically, whilst the attack was underway, the Thousand Sons' focus remained on their lore -- rushing to save what incalculably precious works of sorcery and psychic research they could whilst the righteous, if possibly misplaced retribution of Leman Russ' Legion went unchallenged. Indeed, had a proper defence of Prospero been attempted, more time might have been bought to evacuate the libraries and studies of the Thousand Sons' ultimately costly work.
The planet was ultimately transformed into a blasted ruin, picked clean by millennia of looters and Rogue Traders, after an Exterminatus was unleashed upon it by the Imperium following the Horus Heresy because of its connection to the Thousand Sons and its people's heretical sorcerous heritage. Such a fate befell each of the homeworlds of the Traitor Legions, since each was believed to be a source of Chaotic corruption that could not be cleansed save by utter annihilation.
Temple-Arcologies of Tizca
Towering above the minor pyramids and other lesser structures of Tizca were the eight temple-arcologies. Five of these immense structures housed the vast training facilities, libraries and barracks of the largest of the psyker-Cults of Prospero, as well as the living quarters of the throngs of lesser adepts, servants and extensive defensive fortifications and weapon emplacements. One of the true wonders of the City of Light, each temple-arcology was a city unto itself, as well as a private fortress where each of the great Cults of the Thousand Sons had perfected their individual doctrines and rituals far from the prying eyes of outsiders. Almost ten per cent of the total population of Tizca lived within the precincts of one of these temple-arcologies, and in case of a city-wide catastrophe, they could provide shelter for a far larger share of the civilian population. Within their cavernous halls were stored enough supplies and munitions to sustain the XV Legion and its dependents for several standard years, and the layered districts within their armoured cores would prove all but impossible to take by storm. Any attacker targetting Prospero would need to neutralise these structures quickly or face the prospect of a lengthy and costly siege.
The ninth of these structures stood at the centre of the city, within the sculpted boundaries of Occullum Square. Unlike the other eight, there were no civilians or companies of the Thousand Sons in residence here. A complex of ancillary buildings and lesser pyramids sprawled across the square at its feet, which housed the collected wisdom of Prospero and the Thousand Sons. These structures comprised the Great Library, the most hallowed treasure of Prospero, and the ninth temple-arcology was the Pyramid of Photep, the sanctum of Magnus the Red himself. Few other than the most trusted of the Thousand Sons' officer corps and the elite warriors of the First Fellowship ever entered those halls and witnessed the hidden labours and experiments of the Sorcerer Primarch. In the wake of the utter destruction wrought by the Space Wolves, none will ever know what secrets he uncovered within its halls.
Prospero is the main protagonist and master sorcerer in William Shakespeare's The Tempest. It is also a satellite of the gas giant Uranus in the Sol System.