Alma 52:9

And he also sent orders unto him, that he should fortify the land Bountiful, and secure the narrow pass which led into the land northward, lest the Lamanites should obtain that point, and should have power to harrass them on every side.

Moroni also told him to make the land Bountiful safe. He needed to protect the narrow pass that led north. If the Lamanites got control of that pass, they could attack them from all sides.

He also ordered him to fortify the land of Bountiful and secure the narrow pass that led north, so the Lamanites couldn’t gain that strategic point and use it to attack them from all sides.