Numbers 3:23

"The families of the Gershonites shall pitch behind the tabernacle westward."

Cross References (ranked by relevance)

But the Levites shall pitch round about the tabernacle of testimony, that there be no wrath upon the congregation of the children of Israel: and the Levites shall keep the charge of the tabernacle of testimony.

Numbers 2:17

Then the tabernacle of the congregation shall set forward with the camp of the Levites in the midst of the camp: as they encamp, so shall they set forward, every man in his place by their standards.