Numbers 35:4

And the suburbs of the cities which ye shall give unto the Levites,.... The dimensions and bounds of them were not left to the Israelites, to give what ground they pleased for this purpose, but were fixed to what length they should be: these

[shall reach] from the walls of the city, and outward, a thousand cubits round about; which was half a sabbath day's journey, and pretty near half a mile, which all around a city must contain a considerable quantity of ground, if the city was of any size, as it is certain that some of them given them at least were.