A Calamity is a cataclysmic event that signals the end of an Astral Era, thus leading into a time of hardship known as an Umbral Era. Though there have been seven Calamities total in the history of Eorzea[1], most instances of "The Calamity" refer to the Seventh Umbral Calamity—the descent of Dalamud (the second moon) in the year 1572 of the Sixth Astral Era, leading to the release of Bahamut at the Battle of Carteneau.

Seventh Umbral Calamity

The Seventh Umbral Calamity, often known simply as the Calamity, ended the Sixth Astral Era. Foretold in the Divine Chronicles, the prophesied cataclysm that brought the Seventh Umbral Era was long considered apocryphal.

The Seventh Umbral Calamity was brought about by the Meteor Project of the Garlean Empire—a plan intended to bring the lesser moon Dalamud crashing down onto the realm of Eorzea.

Though the VIIth Legion was routed and Van Darnus defeated at Rivenroad, the lesser moon of Dalamud continued its descent. Archon Louisoix and the Circle of Knowing implored the people of Eorzea to pray to the Twelve, while the Eorzean Alliance gathered to meet what remained of the VIIth Legion at ground zero of Dalamud's impact: Carteneau Flats.

As the Battle of Carteneau waged, the moon broke apart to reveal the Elder Primal Bahamut. Freed from millennia of imprisonment, Bahamut razed the realm in his fury. Louisoix attempted his ritual and failed, but sent the adventurers who aided him away into an aetherial rift. Light engulfed the battlefield, ruining several landscapes.

Since then, Eorzean citizens have recovered, but the effects of the calamity still lingers in the outskirts of society.

Bahamut

Originally one of the First Brood of Midgardsormr, Bahamut perished during the twilight of the Third Astral Era while defending Meracydia from an invasion by the reborn Allagan Emperor Xande who set about his campaign making a covenant with the Cloud of Darkness. Tiamat led her remaining children in summoning a primal in the original Bahamut's image to "resurrect" him; the summoned Bahamut, however, was nothing like the original Bahamut. Despite the new "Bahamut's" efforts, the Ascians taught Xande the means to subdue the Dreadwyrm with the Allagan machine Omega, resulting in the primal being incarcerated in an artificial satellite called Dalamud to collect solar energy for the benefit of the Allagan Empire.

To ensure the primal would remain in place, colossal neuro-links held him in restraint while captive dragons were kept aboard the space station in stasis to keep him summoned perpetually. Having embraced nihilism while brooding over his mortality, a rebellion has begun among the people, Xande tried to summon the Cloud of Darkness to Hydaelyn by channelling the amassed energy from Bahamut into Syrcus Tower. As this exceeded its capacity the excess of energy caused a devastating earthquake that ruined the Allagan civilization and ushered the Fourth Umbral Era.