Numbers 1:49-51

49 Only the tribe of Levi, shalt thou no number, nor the sum of them, shalt thou reckon up, in the midst of the sons of Israel.

50 But do, thou thyself, put the Levites in charge over the habitation of the testimony, and over all the furniture thereof and over all that pertaineth thereto, they, shall bear the habitation, and all the furniture thereof, and they, shall attend thereupon; and, round about the habitation, shall they encamp.

51 And, when the habitation is to set forward, the Levites shall take it down, and when the habitation is to be pitched, the Levites, shall set it up, but the stranger that draweth near, shall be put to death.