Omner was a Nephite city on the east borders by the seashore, named in the account of Amalickiah’s invasion around 67 BC. It was one of the cities Amalickiah captured while Moroni was occupied putting down the king-men and regulating his own people for war; the Lamanites came into the land of Moroni, drove the Nephites from the city of Moroni, and Amalickiah went on taking city after city by the seashore (Alma 51:21-27). Omner is listed in this advance alongside Nephihah, Lehi, Morianton, Gid, and Mulek, all on the east borders by the seashore, and all strongly fortified after the manner of Moroni’s own fortifications, so that they afforded strongholds for the Lamanites once taken (Alma 51:26).
The east-coast region had been settled and fortified at Moroni’s direction: he drove the Lamanites out of the east wilderness, sent inhabitants of Zarahemla to possess the land to the borders by the seashore, and had fortifications erected along the line between Nephite and Lamanite lands (Alma 50:7-11). In the later Nephite recovery, Moroni and Pahoran retook Nephihah and pursued the Lamanites from city to city down to the borders by the seashore, where they were met by Lehi and Teancum (Alma 62:26-32).