The Burning of the Library of Alexandria was an accidental catastrophe that led to the library being mostly burned down by sun god Ra. While fighting the god of darkness, Apophis, Ra's powerful fire managed to push him into the Shadow Realm but burn down the building as well. Thanks to his big mistake, the Egyptian people started to revolt and lose faith in Ra.
Background
Fall of the Rainbow Dimension
With the powers of the Dark One going to his head, the Serpopard Ogdoad Apophis settled in the Rainbow Dimension, a central realm of the Universe. There he commanded the Darkness to tear the Dimension to shreds and he nearly succeeds. The planet Apophis was on was completely destroyed and moat of the surrounding realms. Before the task could be completed, Ra bursts into the Rainbow Dimension and pushes Apophis out of it and into a Wormhole heading towards Earth.
Conflict
Ra and Apophis crash land in the Mouseion in Alexandria, Egypt, destroying part of the building on impact. An explosive battle between the dark god and sun god ensues. Ra slings his Devine fire at Apophis only for him to block it with shadows and bounce it elsewhere in the library. This continues for hours until nearly the entire library is up in flames. Apophis mocks the sun god for his incompetence and inability to protect his worshipers. An angered Ra uses all of the rest of his magic to banish Apophis back to the Shadow Realm, and extracting the powers of the Dark One from him. Ra is left alone in the burning building.
Aftermath
Coverup
As one of the great hubs of knowledge burned to the ground, destroying many of the books within it as well, Ra fleas the scene. However, Roman soldier Gaius Julius Caesar was present during the battle. Wanting to protect the image of a literal god, Caesar takes the blame for the burning, but to little avail. The Egyptian people was able to see past the ruse, and began turning away from Ra, some even starting to hate the Ogdoad.
Massacre of the Egyptians
With the Terrans refusing to prey and worship the sun god, Ra began plotting against them. He sent his daughter, the Ennead Goddess of War, Sekhmet to brutally kill the heretics. However she did not stop at the heretics, and began killing believers and even people outside of Egypt. She was eventually stopped by Ra by him tricking her into drinking a mass amount of alcohol. A drunk Sekhmet returns to her father in Heliopolis humbled and ashamed.