Numbers 2:16-17

The total of the numbered men [in the three tribes on the south side] in the camp of Reuben was 151,450, by their armies. They shall move out second [on the march]. “Then the Tent of Meeting (tabernacle) shall move out with the camp of the Levites in the middle of the [other] camps; just as they camp so shall they move out, every man in his place by their standards.