Numbers 35:9

All the cities which you shall give to the Levites shall be forty-eight cities together with their suburbs.

Concerning the cities which you shall give of the possession of the children of Israel, from the many you shall take many; and from the few you shall take few: everyone according to his inheritance which he inherits shall give of his cities to the Levites.

Speak to the children of Israel, and tell them, 'When you pass over the Jordan into the land of Canaan,

then you shall appoint you cities to be cities of refuge for you, that the manslayer who kills any person unwittingly may flee there.