Great Disaster

"My name is Eriana-3, disciple of the Praxic Warlocks, marked by the Cormorant Seal. Survivor of the great disaster: the day we set out to retake our moon, united in a host of thousands, and found ourselves outmatched by one Hive champion of unspeakable power."

- Eriana-3

The Great Disaster was a battle fought between thousands of Guardians and the Hive to take control of the Moon.

Prelude
Shortly after discovering the Hive during the Battle of Burning Lake, the Vanguard ordered a full-scale assault on the Moon to establish a beachhead. Lord Shaxx, however, warned the Consensus that the Ascendant Swords carried by the Hive Knights were unlike any weapon he'd seen before, and that they should delay the attack.

The Battle
Lord Shaxx's pleas were ignored, and the Guardians who arrived fell by the hundreds, as leading the Hive army was the God-Prince Crota, an invincible Knight who devoured the Light of the Guardians. Mare Imbrium was one of the battlefields, as Crota led one thousand Knights against over five hundred Guardians, easily cutting through them. The legendary Titan Wei Ning was personally killed by Crota here. It was claimed the sky above the region "turned into green fire."

During this campaign, an unknown Titan created the first Thunderlord, along with two other machine guns that came to renown. Though the Thunderlord survived, its counterparts were lost.

Aftermath
In the aftermath, the Vanguard classified the Moon as forbidden, and not to be visited unless absolutely necessary. One of the survivors of the battle, Eriana-3, swore revenge against Crota and assembled a team of Guardians to enter the Hellmouth alone. Only Eris Morn survived that venture.