Numbers 2:17

Then shall move the tabernacle of the testimony, and the camp of the Levites, as the centre division of the camps. As they encamp so they shall take up their march, every man in his rank, according to their companies.

And then the tabernacle of witness shall be set forward, and the camp of the Levites shall be between the camps; as they shall encamp, so also shall they commence their march, each one next in order to his fellow according to their companies.