Onu-Koro
Onu-Koro was the earth engineers' city, where underground isolation created one of Mata Nui's most self-sufficient settlements, until the Bohrok came.

Deep beneath Mata NuiMata Nui (Location)An island created by accident on the Great Spirit's face, home to the Matoran for a thousand years.'s surface lay Onu-KoroKoroThe Koros were the six elemental villages built on Mata Nui after the Great Rescue, on sites the Toa Metru had chosen, each tied to one element and one Turaga., the subterranean settlement of the Onu-MatoranOnu-MatoranEarth-wielding Matoran of the deep who adapted to darkness and built the Matoran Universe's defensive cavalry.. TuragaTuragaFormer Toa who fulfilled their destiny and transformed into leaders. Turaga wield Noble Kanohi masks and weakened elemental powers, guiding their communities. WhenuaWhenuaToa Metru of Earth and later Turaga of Onu-Koro, formerly an Onu-Metru archivist whose career in the Archives shaped his role across the rescue of Metru Nui and the long residency on Mata Nui. led the village with quiet confidence, while Toa OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe. served as its protector. The Great Market drew merchants from across the island, eager to trade for what the Onu-MatoranOnu-MatoranEarth-wielding Matoran of the deep who adapted to darkness and built the Matoran Universe's defensive cavalry. engineers produced. It wasn't a settlement that depended on sunlight or open sky. Onu-KoroKoroThe Koros were the six elemental villages built on Mata Nui after the Great Rescue, on sites the Toa Metru had chosen, each tied to one element and one Turaga. thrived where others wouldn't, in the earth itself.
The Underground City#

WhenuaWhenuaToa Metru of Earth and later Turaga of Onu-Koro, formerly an Onu-Metru archivist whose career in the Archives shaped his role across the rescue of Metru Nui and the long residency on Mata Nui.'s leadership defined Onu-KoroKoroThe Koros were the six elemental villages built on Mata Nui after the Great Rescue, on sites the Toa Metru had chosen, each tied to one element and one Turaga. as something distinct from the surface KoroKoroThe Koros were the six elemental villages built on Mata Nui after the Great Rescue, on sites the Toa Metru had chosen, each tied to one element and one Turaga. in both culture and economy. He described the settlement as a wondrous underground city where MatoranMatoranThe most abundant species in the Matoran Universe, chosen by Mata Nui to inhabit and maintain his cosmic body. came from far and wide to trade at the great Market and admire the work of the engineers. The engineering culture of the Onu-MatoranOnu-MatoranEarth-wielding Matoran of the deep who adapted to darkness and built the Matoran Universe's defensive cavalry. ran deep and carried real prestige. They specialized in mining and construction, pulling valuable resources from the earth that supplied trade goods for the entire island. Toa OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe. stood as protector of this underground settlement, guarding against threats that emerged from the depths of Onu-WahiOnu-WahiThe underground kingdom of Mata Nui, home to the Onu-Matoran and Toa Onua..
Under Fire#
The BohrokBohrokHive-minded mechanical creatures designed to reshape worlds, the Bohrok represent a threat the Toa Mata never expected. invasion brought the first major test to Onu-KoroKoroThe Koros were the six elemental villages built on Mata Nui after the Great Rescue, on sites the Toa Metru had chosen, each tied to one element and one Turaga.'s defenses. When NuhvokNuhvokThe earth-dwelling Bohrok whose rigid nature made them dangerously predictable. swarms erupted from their hives beneath the earth, they attacked the underground settlement directly, seeking to overrun what lay below. But Toa OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe. proved far more capable than the invaders expected. According to BIONICLEBIONICLE: Matoran AdventuresA 2002 GBA platformer where you play as one of six Matoran fighting Bohrok across Mata Nui's islands. Chronicles 2, OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe.'s understanding of the BohrokBohrokHive-minded mechanical creatures designed to reshape worlds, the Bohrok represent a threat the Toa Mata never expected.'s predictable nature let him exploit their weakness: their rigid, autocratic structure made them easy to mislead. He tricked them into submission, holding the line even as other KoroKoroThe Koros were the six elemental villages built on Mata Nui after the Great Rescue, on sites the Toa Metru had chosen, each tied to one element and one Turaga. fell to the swarms. Later, during the events of BIONICLEBIONICLE: Matoran AdventuresA 2002 GBA platformer where you play as one of six Matoran fighting Bohrok across Mata Nui's islands.: Mask of Light, new danger emerged. Three RahkshiBionicle Rahkshi: the Sons of Makuta from Mask of LightRahkshi are armoured hunters made from kraata, the slug-like creatures of the Makuta. Six of them chased the Mask of Light across Mata Nui in 2003. Here's what they are, the different kinds and where they turn up in the films, books and comics. burst through Onu-KoroKoroThe Koros were the six elemental villages built on Mata Nui after the Great Rescue, on sites the Toa Metru had chosen, each tied to one element and one Turaga.'s walls, and OnuaOnuaOnua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe. unleashed an earthquake that buried them under piles of earth, buying time for the villagers to escape.
Compiled from primary sources by Lore Fortress editorial. Reviewed by Joe Garratt, Editor-in-Chief.
Gallery

Images via BIONICLE Wiki (Biosector01)
Sources
- BookBIONICLE Chronicles 2: Beware the Bohrok, The Bohrok invasion and Nuhvok attack on Onu-Koro
- VideoBIONICLE: Mask of Light, The Rahkshi attack on Onu-Koro and scenes in the underground settlement
- GameMata Nui Online Game, Whenua's description of Onu-Koro as a center for engineering and trade
- WikiBiosector01 - Onu-Koro, Comprehensive overview of Onu-Koro's history and significance
Spotted a factual error or a primary source we missed? Email a correction. Every flagged claim gets reviewed.
Followed from this entry

Onu-Wahi
The underground kingdom of Mata Nui, home to the Onu-Matoran and Toa Onua.

Mata Nui (Location)
An island created by accident on the Great Spirit's face, home to the Matoran for a thousand years.

Bionicle Rahkshi: the Sons of Makuta from Mask of Light
Rahkshi are armoured hunters made from kraata, the slug-like creatures of the Makuta. Six of them chased the Mask of Light across Mata Nui in 2003. Here's what they are, the different kinds and where they turn up in the films, books and comics.

Koro
The Koros were the six elemental villages built on Mata Nui after the Great Rescue, on sites the Toa Metru had chosen, each tied to one element and one Turaga.

Onua
Onua was the Toa Mata and Toa Nuva of Earth, a quiet, deliberate warrior whose patience and underground mastery anchored his team across the Matoran Universe.

Whenua
Toa Metru of Earth and later Turaga of Onu-Koro, formerly an Onu-Metru archivist whose career in the Archives shaped his role across the rescue of Metru Nui and the long residency on Mata Nui.
Mentioned in89 entries
Aiyetoro
Aiyetoro was an Onu-Matoran of Metru Nui who became a miner in Onu-Koro on Mata Nui, digging for ore beneath the island and honouring the Virtues of Duty and Destiny.
Azibo
Azibo was an Onu-Matoran prospector of Onu-Koro, the Chief Prospector's most trusted hand and a student of the Principle of Prosperity.
Boxor
Built by Nuparu from a salvaged Gahlok shell, the Boxor was the first Matoran-engineered combat machine and a key resistance asset against the Bohrok swarms.
Cavern of Light
The Cavern of Light was the lightstone mine that supplied Onu-Koro on Mata Nui, opened only with a special key and guarded by the Onu-Matoran Kaj.
Charms
Small carved stones inscribed with the Three Virtues, the six Principles, and the six Kolhii Skills, used as keys to the six Wahi temples on the island of Mata Nui.
Claws (Nuhvok Va)
The paired claws of the Nuhvok Va, which served as their hands, let them dig shallow escape tunnels and doubled as a defensive weapon during the Bohrok swarms' rampage across Mata Nui.
Climbing Claws
Pohatu Nuva's Toa tools, used for climbing the canyons of Po-Wahi, for fighting and pinning foes, and joined together to form the Kodan Ball, until the issue of Adaptive Armor.
Dosne
Dosne is an Onu-Matoran from Onu-Metru who helped build Onu-Koro on Mata Nui, fled it twice, and went back to Metru Nui to help rebuild the city.
Earth Shield
The earth shields were the paired tools of the Nuhvok Bohrok, used to weaken structures from below until they came crashing down.
Ga-Koro Kolhii Team
The Ga-Matoran pair that won the Mata Nui kolhii championship at Ta-Koro, after Turaga Nokama picked Hahli for the team over Kotu.
Ga-Suva
Gali's shrine in Ga-Koro, the floating village's store for her Kanohi and later her Nuva Symbol, whose light came as the Pahrak siege collapsed.
Hau Nuva
The Hau Nuva was the Toa Nuva variant of the Mask of Shielding, capable of protecting both wearer and nearby allies from anticipated physical attack.
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