Dark Calamity

The Shadows embrace Maerus like a mother's love

Whispering sweet nothings to our ears

"Hush, child. It will be over," she said

"It is time for Slumber."

-Book of Ashes: Verse 4 Chapter Void

The Dark Calamity is a phenomenon where the world is swallowed by eternal darkness for centuries, presumably until every life on the world ceased to exist. The first calamity was orchestrated by The Ashen Born, swallowing Maerus and brought upon the Void Callers to eliminate humanity and their creation.

Manifestation

The Moon and Stars vanished in the skies

The Sun was black as it rose

From Darkness they crawl

From Darkness they Called

From Earth they Cry

"The End has come!"

-Book of Ashes: Verse 13 Chapter Void

Darkness enshroud the world like a veil. The Sun turned Black, burning every life on the world. The Void Callers emerged from the darkness, devouring everything in their way indiscriminately. No light can be lit, not from the torches, the lamps, the candles. Nothing can pierce the darkness, and if they do, they will risk being found by the Void Callers and devoured.

Type

Metaphysical, Demonic

Symbolism of Number 4

In Japanese, Taiwan and China, they believed that number 4 is an unlucky number which symbolizes "death". This is due to in their language, the word "shi" shares the same meaning with number 4 and death.
The first quote from Book of Ashes, it can be founded in Verse 4. Hence, the verse alludes to the death of life in Maerus.

Symbolism of Number 13

In the tarot, 13 brings the test, the suffering and the death. It symbolizes the death to the matter or to oneself and the birth to the spirit: the passage on a higher level of existence. 
The second quote can be founded in Verse 13, alluding to the suffering the people in the old world from the Dark Calamity. It can also allude to Maerus' destruction led to the creation of Frantumare and brought forth new life and generation in the current world.