Deuteronomy 19:1-3

When the Lord thy God shall roote out the nations, whose lande the Lord thy God giueth thee, and thou shalt possesse them, and dwell in their cities, and in their houses,

Thou shalt separate three cities for thee in the middes of thy lande which the Lord thy God giueth thee to possesse it.

Thou shalt prepare thee the way, and deuide the coastes of the land, which the Lord thy God giueth thee to inherite, into three parts, that euery manslayer may flee thither.