In addition to the physical buildup of defenses, Moroni analyzed the lay of the lands and the seas to fortify his people against the enemy. He drove out the Lamanites from inside his line of defense and placed his armies in position to protect the people against the power of the Lamanites armies (vv. 11–12).
The land of Nephi running from the east sea to the west (v. 8) should again be qualified geographically. The land did not necessarily run to the west sea, but to the west. The wilderness on the west may have ended the straight course. Similarly, the west sea did not necessarily run “by the head of the river Sidon,” but the fortified line was “between the Nephites and the Lamanites, between the land of Zarahemla and the land of Nephi, from the west sea” (v. 11 compare Alma 22:32; Helaman 4:7). If the sea ran by the head of the river, it should have been to the south not the west. So much for geography until we get a fuller record.