Crystal pillar (Final Fantasy XIII)

The crystal pillar is a large crystal structure in Final Fantasy XIII and Final Fantasy XIII-2 that was erected in the conclusion of Final Fantasy XIII to stop the fall of Cocoon. Its creation marks the beginning of the AF calendar.

Datalog
''During the catastrophe of 0 AF, a gigantic crystal pillar appeared and caught Cocoon in its embrace. This miracle was the work of Fang and Vanille, two women who sacrificed themselves to achieve the impossible.''

''In the centuries that follow, however, erosion weakens the massive structure. This second threat to Cocoon triggers a war among its people, and the resulting violence brings the sphere crashing to the ground. The apocalyptic age in which Noel was born is what remains of the world after those tragic events come to pass.''

Final Fantasy XIII
At the end of Final Fantasy XIII, Vanille and Fang transform into Ragnarok after the party defeats Orphan, thus robbing Cocoon of its power source and sending the floating world plummeting towards Gran Pulse. Ragnarok crystallizes Cocoon's shell and builds a crystal pillar from the ground up to support the structure. In doing this, the duo crystallizes themselves within the pillar and enter crystal stasis.

Final Fantasy XIII-2
In 10 AF at the Yaschas Massif, it is discovered through a vision recorded in an Oracle Drive by the seeress Yeul that the pillar holding Cocoon will eventually crumble, sending the crystallized Cocoon plummeting towards the surface of Pulse. According to Noel, it is the event that marks the end of days to human civilization.

The vision also depicts that Cocoon's fall is apparently caused by Caius Ballad. Serah and Noel set out to save the future and prevent Cocoon from falling, while Hope makes it the Academy's top priority to prepare for the event that is set to take place hundreds of years in the future.

When Serah and Noel travel to Sunleth Waterscape in 300 AF, they find a giant flan eroding the crystal pillar and come to the conclusion that the flan would eventually weaken the pillar enough for it to send tremors on the ground, making people nervous and eventually causing them to break out into a war, which would culminate in the pillar's full destruction. Serah and Noel solve the paradox and defeat the flan, preventing this scenario from happening.

In the year of the prophecy, 500 AF, Serah and Noel stop Caius from destroying Cocoon and Hope's Bhunivelze, and defeat him in Valhalla, restoring the timeline. Meanwhile, Hope and Sazh remove Fang and Vanille from the pillar moments before it crumbles, sending Cocoon falling towards Gran Pulse's surface.

Trivia

 * The logo of Final Fantasy XIII and the necklaces of Serah and Snow Villiers are in-game allusions to the crystal pillar.
 * It is mentioned in the Brain Blast quiz that after the fal'Cie's rule was over, the people who stayed on Cocoon wanted to find a new god to worship in their place. The design of the god worshiped on Cocoon in the era of Academia -400 AF- is said to be based on the crystal pillar.

Pilier de cristal