The Purge

The Purge is the name given to a set of policies layed out in 4688 AY by Aurean emperor Tiberius XVII intended to stamp out worship of any of the gods outside of The Divine Five. Over the next hundred and fifty years these policies would lead to the destruction and conversion of numerous temples, the execution of thousands of priests, and a series of rebelions that would eventually lead to the near total collapse of the empire in the 49th century.
Tiberius had come to the throne after overthrowing Vollinan II, known sometimes as Vollinan the Undying, the lich emperor who had ruled the empire for over three hundred years and was known for the brutal treatment of his subjects. Vollinan had been a worshiper of Thalassar, the god of undeath, and had even begun to present himself as a god, though his cult was small and short lived. After coming to the throne, Tiberius blamed many of the problems the empire had faced under Vollinan on moral failings, and decided to purge the empire of the worship of gods whose ideals he saw as incompatible with what he planned for the empire.
He eventually settled on a group of five dieties, Deyallor, Nerralla, Athis, Ithren, and Endil, who together would become known as the Divine Five. For the remainder of the Purge, worship of any other god was brutally punished. The Purge was ended in 4856 AY by emperor Matteran I, but it's legacy is still felt within the empire and it's former lands to this day.