Alma 49:2 states that as part of Moroni's effort to fortify the city of Ammonihah, "they had cast up dirt round about to shield them from the arrows and the stones of the Lamanites." According to Michael and June Hobby, we can compare the descriptions in the Book of Mormon with descriptions of the Maya site of Becan, located in Campeche, Mexico. The report quoted is "Defensive Earthworks at Becan, Campeche, Mexico, Implications for Maya Warfare" by David L. Webster. The report is an outgrowth of the National Geographic Society - Tulane University program of research in Campeche, directed by Dr. E. Wyllys Andrews IV of the Middle American Research Institute. Webster reports:
Despite the dense forest cover, Ruppert and Dennison were able to recognize and map with considerable accuracy the three basic features of the defensive system: the ditch, the parapet, and the causeways. . . . The basic feature of the defenses, the ditch, was originally a deep trough with an average width of about sixteen meters (about 48 feet). To judge from the bedrock outcrops which are still visible, the sides of the trough must have been vertical or near vertical, steep enough to keep attackers from clambering up them. . . . The extreme width of the defenses provides additional protection, for heavy missiles can be thrown only with great difficulty from the embankment to the outer edge of the ditch in most places. To throw uphill from the outside is almost impossible. . . . The ditch has a total length of about 1,890 meters (about 1.2 miles). . . . The actual width (of the ditch), except near the causeways, is never less than twelve meters and may reach twenty-seven meters with an average of about sixteen meters (forty-eight feet).
[Michael and June Hobby, Proofs of the Book of Mormon, pp.36-37]
Alma 49:2 They had cast up dirt round about to shield them from the arrows ([Illustration]): The most effective system utilized by the Nephites under Moroni's command was the Ditch and Parapet. This system was constructed by digging a deep ditch of considerable width, and heaping the excavated soil along the ground adjacent to the ditch on the inner side. In this manner, for each unit of depth excavated, a unit of height was generated. [Michael and June Hobby, Proofs of the Book of Mormon, p.32]
Alma 49:2 They had cast up dirt round about to shield them from the arrows ([Illustration]): By completely encircling the exposed portions of the site with the ditch, leaving causeways across it only at selected points of entrance, the defensibility of the site would be maximized. [Michael and June Hobby, Proofs of the Book of Mormon, p.33]