In Alma 43:22 it says that “the Lamanites departed out of the land of Antionum into the wilderness and took their journey round about in the wilderness, away by the head of the river Sidon, that they might come into the land of Manti.” According to John Sorenson, from the land of Antionum to the land of Manti, a long distance is indicated by the elapsed time. While the Lamanites went “round about,” indicating a curved route, there was time: (1) for Moroni to have spies follow them to determine their course (Alma 43:23); (2) for the spies to return to Moroni’s camp in Jershon; (3) for Moroni to send men from Jershon to Zarahemla to get guidance from Alma (Alma 43:23); (4) for the men to return to Jershon (Alma 43:24); (5) for Moroni and part of his army to travel “over into” the land of Manti (Alma 43:25); and (6) for Moroni to set an ambush and wait a certain period of time. [John L. Sorenson, The Geography of Book of Mormon Events: A Source Book, F.A.R.M.S., pp. 256-257]
According to John Sorenson’s Mesoamerican setting, two routes were available to the Lamanites between the land of Antionum and the land of Manti; they could have traveled over either. One slices through the vast Chiapas rain forest wilderness via a network of jungle valleys. The other way skirts the rough country, going all the way to the Usumacinta River and following it upstream. The second is much longer but more sensible to travel, for there would have been settlements along the way to supply food, and the route was sure. The wilderness way, while feasible, went through some of the toughest country in all Mesoamerica, which was mainly unpopulated throughout the period we are talking about. The heart of this mountainous section is still called “el desierto de los Lacandon” (the wilderness of the Lacandon Indians). Either route taken by the Lamanite army would have allowed Moroni’s forces time enough to reach Manti first. [John L. Sorenson, An Ancient American Setting For the Book of Mormon, F.A.R.M.S., p. 256]
Geographical [Theory Map]: Alma 43:4-22 [War in Antionum] & Jershon--Lamanites Depart towards Manti (18th Year)