Pre-exilic biblical texts describe Levites as landless priests who can serve in any holy site. The origin of this status can be found in ancient times, when the tribe of Levi lost control of their territory in the Transjordan, but remained in the vicinity serving in the Nebo temple, where their ancestor Moses was buried.This seems as plausible as the various other reconstructions of the origin and history of the Levites. Our sources are incomplete and contradictory.
Some PaleoJudaica posts on the subject are here, here, here, here, here, and here.
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