Perhaps the Gothic Wars?
AI generated example:
The War of the Seven Colleges
Later Hermetic scholars agreed that no disaster before the Schism War inflicted such lasting ruin upon European magic as the Gothic War. The Roman magical traditions, once united in reverence for Mercury and the ancient rites of the Empire, had long since fractured into rival colleges. When Belisarius crossed into Italy, those rivalries became open war.
The Collegium Ravennatis proclaimed that Justinian had been chosen by Providence to restore the Empire, and lent invisible aid to the imperial armies. Against them stood the old senatorial circles of Rome, together with the Gothic augurs and Etruscan haruspices, who judged the Ostrogothic kingdom to be the last lawful heir of Rome. Others remained neutral only briefly before being drawn into the struggle by old feuds or desperate alliances. Before long every siege concealed another siege, every battle another battle, unseen by mundane eyes.
The chroniclers record only strange fortune. Belisarius repeatedly escaped destruction through decisions that even his own officers considered inexplicable. Totila's armies marched through provinces where resistance seemed to melt away overnight. Sibyls, prophets and visionaries appeared in every camp. Neither side suspected how many of these were merely the shadows cast by the hidden war.
As the years passed, restraint vanished. Rituals once reserved for the greatest festivals of Mercury were turned to war. Rivers were cursed to flood the lands of enemies. Harvests withered beneath invisible maledictions. Ancient guardian spirits were bound into military service. Regiones were forced open to shelter refugees or conceal armies, and many never closed again. Quaesitorial tradition maintains that several of the enduring magical wastelands of Italy date from these workings, though the mundanes remembered only famine.
Procopius wrote simply that "the country lay everywhere deserted" and that the plague came when "the whole human race came near to being annihilated." He tells of burial rites abandoned, cities emptied, and whole districts falling silent. He even records that "apparitions of supernatural beings in human guise were seen by many persons," and that those who encountered them immediately sickened. To the learned of later centuries these words were no mere superstition. They were the testimony of a man who witnessed the invisible war without possessing the language to describe it.
Then came the plague.
The survivors always insisted that it was not summoned by magic. Yet the magical war had already stretched the fabric separating the Realms. Thousands died each day without burial. Ghosts wandered leaderless through deserted streets. Covenants that had stood since the days of Augustus found themselves surrounded not by enemies but by the restless dead. Divine miracles multiplied in answer to desperate prayers. Infernal spirits fed upon despair, appearing in visions throughout Italy and whispering that the world itself had entered its final days. Even Procopius, no credulous monk but an imperial secretary, preserved the reports of supernatural visitants walking openly among the dying.
It was afterwards said that Justinian himself had become the prize in a contest among powers greater than men. Procopius dared write that the Emperor was "a demon in human form," recounting tales that his head vanished from his shoulders, that his face dissolved into a featureless void, and that a holy monk fled the imperial throne, declaring that he had seen not an emperor but the Chief of Demons seated there. Whether these were merely the ravings of a bitter historian or distorted memories of infernal meddling has never been settled among Hermetic scholars.
When at last the Lombards descended into Italy, there was scarcely anyone left to oppose them. The seven colleges had annihilated one another. Their libraries burned with the cities they had sworn to protect. Their apprentices had perished in plague. Their sanctuaries stood abandoned amid wilderness where wolves nested in former vineyards. Of the hundreds of Roman magi believed to have lived at the opening of Justinian's reign, later Bonisagus could discover only a handful of broken survivors, each guarding a few fragments of a tradition no longer whole.
Thus, say the oldest Quaesitorial commentaries, did the Roman magical world perish—not because mundane armies proved stronger than wizards, but because the magi chose to make the fate of kingdoms their own. When the kingdoms fell, so too did every covenant that had bound its destiny to crown or empire. Bonisagus and Trianoma needed no better lesson when they wrote that a magus must not interfere with the affairs of mundanes, lest the ruin of the mundanes become the ruin of all magi.
