Halakhah su Numeri 35:1

And that is that He commanded us to give cities to the Levites to dwell, since they do not have a portion and inheritance in the Land. And that is His, may He be blessed, saying, "And they shall give to the Levites [...] cities to dwell" (Numbers 35:1). And these cities of the Levites are cities of refuge that provide a shelter according to the description specified in Tractate Makkot. (See Parashat Masei; Mishneh Torah, Sabbatical Year and the Jubilee 13.)