Timeline of World History

This is a list of historical events that occur in Made In Abyss. All dates are approximate, and calculated back from the start of the series (or the present time). Some dates may be incorrect due to time dilation caused by the Abyss.

6000 years ago:
 * The first known group of Praying Skeletons are entombed within the Burial Tower.

4000 years ago:
 * The Wind-Riding Windmills in the 2nd layer were built at least 4000 years ago and were used to catch updrafts.
 * The second known group of Praying Skeletons are entombed within the Burial Tower.

2000 years ago:
 * The third (and most recent) known group of Praying Skeletons are entombed within the Burial Tower.

150 years ago in time on the 6th layer :
 * According to Wazukyan, the village of Ilblu is established. It has been much longer than this on the surface, and Wazukyan's perception of time has been altered by the Abyss to the respective layer.
 * Some time later, Irumyuui's last child meets Gaburoon, learning the abyssian language and the meaning of value.

1900 years ago:
 * The Abyss is discovered by the future inhabitants of Orth. It may have been discovered earlier by other groups, suggested by Ganja arriving before the official discovery 1900 years ago, but this is unknown.

250 years ago
 * A letter labeled the Hariyomari's Collection containing the first and only account relating to the curse of the 7th layer is found within the 1st layer, it is then suddenly lost as it was being deciphered.

50 years ago:
 * Rumours begin circulating about Ozen, suggesting that she has been a White Whistle Delver for at least 50 years, and was presumably born at least a decade or two before that.

Unknown dates:
 * Ozen meets the child Lyza and steadily grows attached to her.

15 years ago:
 * Bondrewd obtains the Special Grade Artifact Zoaholic.

12 years ago:
 * Ozen, Torka and a pregnant Lyza are dispatched on a special mission to the 4th layer to retrieve the Unheard Bell.
 * Torka does not survive the mission but the stillborn Riko is revived by the Curse-Warding Box.

10 years ago:
 * Bondrewd establishes the Forward Operating Base Ido Front over the remains of an ancient altar in the deepest part of the 5th layer, starting his experiments with children gathered from places like Sereny.
 * Lyza takes a disciple, leaving Riko in his care at Belchero Orphanage before going on her Last Dive to the 6th layer, asking Ozen to guide her daughter if she ever wants to descend herself.

Unknown dates:
 * After successfully receiving the blessing of the Abyss, Nanachi starts working for Bondrewd, experimenting on Mitty.
 * Bondrewd starts raising Prushka, the curse-affected daughter of an Umbra Hand.
 * Bondrewd visits Ilblu, taking Mitty with him, and Belaf trades most of his body to make a perfect copy of her.

8 years ago:
 * An attempt to use an airship to descend into the Abyss ends in failure. It is possible this attempt was the one that led to the crash in which Marulk was invoved.

7 years ago:
 * Mio visits Orth, encountering a 5-year-old Riko and her pet dog, Reg.

Unknown dates:
 * Nanachi escapes Ido Front, settling at the edge of the 4th layer, trying to find a way to kill Mitty.
 * Prushka starts helping Bondrewd with developing cartridges and treating failed Umbra Hands.
 * After living with her for a while, Reg leaves Faputa to carry out his mission.
 * Srajo and Hail Hex pass through the Ido Front. She is confronted by Bondrewd and the Umbra Hands, while attempting to take her last dive.

Start of the story:
 * Reg, having reached the 1st layer, saves Riko from a Crimson Splitjaw and loses his memories.

2 months later:
 * Hablog receives Lyza's whistle and notes at the Seeker Camp and brings them to the surface on the Resurrection Festival, giving the whistle to Riko. A few days later Riko and Reg descend into the Abyss. 2 days after Reg and Riko's departure, Kiyui gets extremely ill along rampant rumors of the Birthday-Death Disease.

Unknown dates:
 * In the anime adaptation, by the time the Mail Balloon reaches Nat the town of Orth has already been evacuated with only delvers remaining.