According to The Book of Mormon

Book of Mormon

The Book of Mormon is a sacred text of the Latter Day Saint movement that adherents believe contains writings of ancient prophets who lived on the American continent from approximately 2600 BC to AD 421. It was first published in March 1830 by Joseph Smith, Jr...

, the land of Antionum was located east of the river Sidon and east of Zarahemla, south of the land of Jershon , and north of the wilderness which was full of the Lamanites and which probably included the land of Siron . Antionum also bordered on the seashore, apparently to the east of the land.

The name Antionum was given the land by the Zoramites who gathered and settled the area. When Alma and his brethren went to the land to preach to the Zoramites they were surprised to find that the Zoramites had built synagogues and astonished at their unusual form of worship . Those who believed in the words of Alma and his missionary companions were cast out of the land and went north to the land of Jershon to live among the people of Ammon, the Lamanite converts .

The Zoramites eventually allied with the Lamanites in an attempt to overthrow the Nephite government (as had done Amlici). The combined Zoramite/Lamanite army gathered in the land Antionum as the Nephites gathered in the land of Jershon . In large part due to inferior defensive technology, the Lamanites were afraid to face the Nephites at that juncture, so they departed the land of Antionum into the wilderness, toward the land of Manti where a battle ensued .

The hill Onidah was located in the land of Antionum and was the site where Alma and Amulek taught the Zoramite poor .