Fire of Myrmidon

The Fire of Myrmidon was a massacre the took place on the night of the 2nd of Nero, 1063, invoked through Gottard Yelver's betrayal of the Contingency, in which the city of Myrmidon was burnt by forces upholding the Contingency.
The attack was planned and led by Mastiff, and forces of numerous tribes and city-states participated in the assault, as well as the four Chaptersires, who played a pivotal role in the attack's success.
While the Fire of Myrmidon is considered grisly, reprehensible, and painful to remember, it is also commonly regarded as an event that saved the world.