From Halopedia, the Halo wiki
A Kiva was a type of settlement on the human colony world of Reach. Situated in the harsh wilderness of the planet, they were arranged in small communities with the inhabitants making a living out of farming or handicrafts.
Built mostly of concrete, kivas were utilitarian in design, but nonetheless designed to be comfortable. Most of the structures were rounded, circling a central courtyard, and often partially subterranean. Due to their remoteness, kivas were often self-sustaining, located outside power grids and powered by their own wind turbines. Visegrad had a community of kiva homesteads.
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