Numbers 35:4-5

4The common-land of the cities which you will give the Levites shall extend from the wall of the city outward a thousand cubits all around.

5And you shall measure outside the city on the east side two thousand cubits, on the south side two thousand cubits, on the west side two thousand cubits, and on the north side two thousand cubits. The city shall be in the middle. This shall belong to them as common-land for the cities.