Numbers 3:36-39

36And the appointed guard duty of the sons of Merari involved the frames of the tabernacle, the bars, the pillars, the bases, and all their accessories; all the service connected with these; 37also the pillars around the court, with their bases and pegs and cords. 38Those who were to camp before the tabernacle on the east, before the tent of meeting toward the sunrise, were Moses and Aaron and his sons, guarding the sanctuary itself, to protect the people of Israel. And any outsider who came near was to be put to death. 39All those listed among the Levites, whom Moses and Aaron listed at the commandment of the LORD, by clans, all the males from a month old and upward, were 22,000.