Defensive ditches are excavations surrounding fortified places, paired with raised banks and entrances. The Lamanites could not enter Nephite forts except “by the entrance, because of the highness of the bank which had been thrown up, and the depth of the ditch which had been dug round about” (Alma 49:18).
When the Lamanites could not obtain power over the Nephites by the pass, they began to dig down their banks of earth to make a pass for their armies. Stones and arrows swept them off, and “instead of filling up their ditches by pulling down the banks of earth, they were filled up in a measure with their dead and wounded bodies” (Alma 49:22).
By Moroni’s orders, Teancum caused the Lamanites to dig a ditch around Bountiful and build a breastwork of timbers upon its inner bank. They cast dirt from the ditch against the breastwork until they had encircled Bountiful with “a strong wall of timbers and earth, to an exceeding height” (Alma 53:3-4).