Compare a Book of Mormon account (Alma 49:18-20) from around 70 B.C. with the description of Dr. Webster above:
18 Now behold, the Lamanites could not get into their forts of security by any other way save 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, save it were by the entrance.Captain Moroni in the Book of Mormon used such fortifications throughout Nephite lands, as explained in Alma 50:1-4 (ca. 72 to 60 B.C.):
19 And thus were the Nephites prepared to destroy all such as should attempt to climb up to enter the fort by any other way, by casting over stones and arrows at them.
20 Thus they were prepared, yea, a body of their strongest men, with their swords and their slings, to smite down all who should attempt to come into their place of security by the place of entrance; and thus were they prepared to defend themselves against the Lamanites.
1 And now it came to pass that Moroni did not stop making preparations for war, or to defend his people against the Lamanites; for he caused that his armies should commence in the commencement of the twentieth year of the reign of the judges, that they should commence in digging up heaps of earth round about all the cities, throughout all the land which was possessed by the Nephites.A related description is in Alma 533-5:
2 And upon the top of these ridges of earth he caused that there should be timbers, yea, works of timbers built up to the height of a man, round about the cities.
3 And he caused that upon those works of timbers there should be a frame of pickets built upon the timbers round about; and they were strong and high.
4 And he caused towers to be erected that overlooked those works of pickets, and he caused places of security to be built upon those towers, that the stones and the arrows of the Lamanites could not hurt them.
5 And they were prepared that they could cast stones from the top thereof, according to their pleasure and their strength, and slay him who should attempt to approach near the walls of the city.
6 Thus Moroni did prepare strongholds against the coming of their enemies, round about every city in all the land.
3 And it came to pass that after the Lamanites had finished burying their dead and also the dead of the Nephites, they were marched back into the land Bountiful; and Teancum, by the orders of Moroni, caused that they should commence laboring in digging a ditch round about the land, or the city, Bountiful.The breakthrough discoveries of Webster and others at Tulane University were soon followed by related findings which fueled a paradigm shift in our understanding of the prevalence of warfare in ancient Mesoamerica. Other findings have confirmed the use of palisaded fortifications (palisade = fence of "pales" or pointed sticks made as a defensive barrier, according to the American Heritage Dictionary), ditches, and earthen walls. John Sorenson summarizes these Mesoamerican findings as of 1984:
4 And he caused that they should build a breastwork of timbers upon the inner bank of the ditch; and they cast up dirt out of the ditch against the breastwork of timbers; and thus they did cause the Lamanites to labor until they had encircled the city of Bountiful round about with a strong wall of timbers and earth, to an exceeding height.
5 And this city became an exceeding stronghold ever after; and in this city they did guard the prisoners of the Lamanites; yea, even within a wall which they had caused them to build with their own hands. Now Moroni was compelled to cause the Lamanites to labor, because it was easy to guard them while at their labor; and he desired all his forces when he should make an attack upon the Lamanites.
More than one hundred fortified sites are now known. Ray Matheny's work at Edzna revealed a large, moated fortress dating to around the time of Christ . Loma Torremote in the Valley of Mexico was a palisaded hilltop settlement by about 400 B.C.  Part of the three kilometers of defensive walls at famous Monte Alban dates before 200 B.C.  The core of Los Naranjos in western Honduras was entirely surrounded by a big ditch sometime between 1000 and 500 B.C.  Besides the actual sites, graphic art, remains of weapons, and warrior figurines have been found for many periods. So have stone walls. (Compare Alma 48:8)  And the public skull-rack (Aztec tzompantli), used at the time of the Conquest by the Aztecs to strike fear into the hearts of potential rebels against their military control, has now been found in Cuicatlan Valley of Oaxaca dating from before the time of Christ. Further support comes from other recent discoveries about palisade-like structures. Richard Hauck, who is LDS, describes a finding in a Guatemalan valley near Coban which he tentatively correlates to a Book of Mormon location ("Ancient Fortifications and the Land of Manti," This People, Summer 1994, pp. 46-55). He describes how easy it has been for researchers to overlook the remnants of dirt and timber structures, but discusses the trenches, the soil changes, the growth of aligned trees, and other clues that point to their previous existence. The site he discovered, in addition to extensive arrays of palisades, also had an identifiable long and narrow pass, consistent with Book of Mormon descriptions, lined with palisades for a long distance, apparently presenting the only way into the fortified area. Attacking armies entering the pass would be prey to defenders along the palisades. Although the identification of Hauck's site with the land or city of Manti is debatable, there continues to be strong evidence that the military fortifications described in the Book of Mormon are consistent with the most recent discoveries in Mesoamerica - and inconsistent with long-held "expert" opinion prior to the radical paradigm shift that began in the 1970s.
"Increasingly, it is apparent that war practices in use when the Europeans arrived go back to the very early history of Mesoamerica. Yet as late as ten years ago, most of the published descriptions of early life in the area directly contradicted this view."(Ensign, Sept. 1984, p. 33.)
References cited by Sorenson:
1. Ray T. Matheny, D. L. Gurr, D. W. Forsyth, F. R. Hauck, Investigations at Edzna, Campeche, Mexico, Vol. 1, Part 1: The Hydraulic System (Brigham Young University, New World Archaeological Foundation, Paper 46, 1983), pp. 169-191.
2. "Current Research," American Antiquity, 45 (1980), p. 622.
3. Richard E. Blanton and S. A. Kowalewski, "Monte Alban and after in the Valley of Oaxaca," in J.A. Sabloff, ed., Supplement to the Handbook of Middle American Indians, Vol. 1, Archaeology (Austin: University of Texas Press, 1981), p. 100.
4. Claude F. Baudez and Pierre Becquelin, Etudes Mesoameriques, Vol. 2, Archaeologie de los Naranjos, (Mexico: Mission Archaeologique et Ethnologique Francaise au Mexique, 1973), pp. 3-4.
5. Angel Palerm, "notas sobras las Construcciones Militares u la Guerra en Mesoamerica," Anales del Instituto Nacional de Antropologia e Historia, (Mexico), 7 (1956), p. 129; and Webster, op. cit., p. 98.
6. Charles S. Spencer and Else M. Redmond, "Formative and Classic Developments in the Cuicatlan Canada: A Preliminary Report," in Robert D. Drennan, ed., Prehistoric Social, Political, and Economic Development in the Area of the Tehuacan Valley: Some Results of the Palo Blanco Project, University of Michigan, Museum of Anthropology Technical Reports, no. 11 (Research Reports in Archaeology, Contribution 6), 1979, p. 211.
Joseph Smith had no military experience when the Book of Mormon was published (apart from being threatened by mobs and thugs). Certainly forts of timber were built by armies in the early days of the United States, but I am unaware of anything quite like the trench and palisade systems described in the Book of Mormon that Joseph would have known about and could have borrowed from his own experience to fabricate the Book of Mormon. Indeed, even a cursory reading of the war chapters in the Book of Mormon reveals that the battles there are quite foreign to anything a farm boy in New York would have experienced. The accuracy of realistic detail, problems with logistics, rebellion, prisoners of war, morale, spies, etc., reflect authorship by someone intimately familiar with real ancient battle. Accurately describing ancient fortifications in Mesoamerica is just one tiny part of the military mosaic that reflects ancient authorship of the Book of Mormon. And again, recall that the whole idea of significant warfare in ancient Mesoamerica was dismissed by the experts until about 20 years ago.