Prospero was the shining homeworld of the Thousand Sons, a world of learning and sorcery unlike any other in the early Imperium. Its principal city, Tizca, the City of Light, was a place of crystal pyramids and vast libraries where knowledge was prized above all, and where the psychically gifted gathered under the protection of the primarch Magnus the Red.
Under the Thousand Sons, Prospero flourished as a sanctuary for scholars and psykers, its people delving into mysteries that the wider Imperium feared and forbade. This pursuit of forbidden lore would prove its undoing. When Magnus used sorcery to warn the Emperor of a brewing treachery and shattered a great work upon Terra in doing so, he was branded a heretic, and a punitive force was dispatched to bring the world to heel.
The Space Wolves fell upon Prospero in a storm of fire, and Tizca's towers were cast down amid slaughter and betrayal. The burning of the world drove the survivors into the arms of Chaos, sealing the Thousand Sons' fall to the Dark God Tzeentch. Today Prospero is a ruin, its glories reduced to ash and memory, remembered as a tragedy of knowledge punished and a turning point in the long war for the soul of humanity. Its fate is recounted more fully in the annals of Prospero.