The Oblivion Crisis, also known as the Great Anguish, was a total war between the Daedra and the population of Tamriel. It began with the assassination of Uriel Septim VII and all of his known heirs. Shortly afterward, Oblivion Gates to the Deadlands opened across Tamriel and Daedra poured out as the result of a fanatical cult of worshippers of Mehrunes Dagon known as the Mythic Dawn. Widespread devastation and casualties resulted across entire provinces. The Daedra besieged Skyrim, and laid waste to the Old Holds. In Black Marsh, the Hist called back many Argonians to fight off the Daedra. The Daedric commanders closed many gates to stop the united Argonians from entering. In Cyrodiil, the city of Kvatch was entirely destroyed.
Adril Arano, a Second Councilor of Raven Rock in the late Fourth Era, claimed that the Empire pulled its forces out of Morrowind during the Crisis. However, this contradicts the words of High Chancellor Ocato himself during the Crisis, who stated that Cyrodiil and cities such as Bruma were virtually defenseless precisely because he was both unable and unwilling to pull any troops out of the other provinces. Indeed, the Imperial Province was left almost entirely to its own devices, and no foreign legions were ever found within Cyrodiil for the entirety of the Crisis or its immediate aftermath. Still, a history of the Raven Rock colony records that the bulk of the Imperial Guard stationed there was recalled to Cyrodiil from the then-Nordic Solstheim, implying Ocato had no such qualms when it came to areas that did not have Oblivion Gate sightings.
The Empire was near collapse, but Uriel VII's illegitimate son, Martin Septim, ended the invasion with the help of a mysterious hero, but the cost was enormous. Martin, the last of the Septim bloodline, sacrificed himself and the Amulet of Kings to become an Avatar of Akatosh and cast Mehrunes Dagon back into Oblivion. This event marked the end of the Third Era and the beginning of the eventual disintegration of the Third Empire.
- Sack of Kvatch: Gates to Oblivion were opened outside Kvatch, from which a horde of Daedra and a siege crawler emerged to overwhelm the guard and sack the city. Much of the population was killed, including Count Ormellius Goldwine and Saint Jiub. After the city was occupied by the Daedric forces, most of the gates were closed, leaving only one lesser gate blocking the city's gates. This gate was eventually closed by a mysterious hero who would later be dubbed the Hero of Kvatch, who then helped the remaining city guard retake the city.
- Fall of Ald'ruhn: The city of Ald'ruhn was destroyed by the Daedra. In an attempt to defend the city, the Redoran resurrected the Ald Skar Emperor Crab, which also fell.[UOL 1]
- Collapse of the Crystal Tower: The Crystal Tower on the Summerset Isle, the bastion of all magical learning before the Arcane University was built, was destroyed by Mehrunes Dagon's invading Daedra, despite the efforts of the powerful Altmer wizards.
- Defense of Bruma: Martin Septim led an army of Cyrodilic city guards to victory over the invading Daedric hordes. A statue was erected within the city's walls, in honor of the lone hero who charged into Oblivion in order to shut the Great Gate and prevent the destruction of Bruma.
- Battle of the Imperial City: High Chancellor Ocato, Martin Septim, his Blades and Imperial Legionary escorts fought their way through an Oblivion-besieged Imperial City. During this battle, dozens of Oblivion Gates opened around the city and the Daedric Prince Mehrunes Dagon himself appeared, marking the fall of the barriers between Oblivion and Nirn. The battle ended when Martin Septim, in a desperate last ditch effort, shattered the Amulet of Kings and became the Avatar of Akatosh. The Avatar banished Dagon back into Oblivion, ending the Oblivion Crisis. The Avatar turned to stone, killing Martin, but also leaving a permanent reminder of Martin's sacrifice.
- Rising Threat — Lathenil of Sunhold
- Tutorial quest in Oblivion
- Main Quest in Oblivion
- Rumors in Oblivion
- The Infernal City — Gregory Keyes
- Breaking the Siege of Kvatch and The Battle for Castle Kvatch quests in Oblivion
- Adril Arano's dialogue in Dragonborn
- Chancellor Ocato's dialogue in Oblivion
- Events of Oblivion
- History of Raven Rock, Vol. I — Lyrin Telleno
- Light the Dragonfires quest in Oblivion
- Defense of Bruma and Great Gate quests in Oblivion
Note: the following references are not from official sources. They are included to provide a rounder background to this article, but may not reflect established lore.
- The Fall of Ald'Ruhn — Michael Kirkbride