To supply the earth to build a strong parapet and its associated structures, an excavation was carried out in the immediate area. This excavation was usually incorporated into the defensive plan, and made to obstruct the movements of the enemy or protect the defenders as much as possible. An exterior excavation was called a ditch, while an interior one was call a trench. Military practice based on two centuries of experience had produced a set of proportions of slope and extent called the ordinary profile.

General rules of thumb as to how long it would take to construct earthworks of a given size are frequently quoted in the textbooks. Many of these rules are directly applicable to the defenses of the Alamo.

Gun positions had their own specific terms. A gun firing over the top of a wall from a raised earthen platform was said to be on a barbette. Barbettes were usually placed in the corners of defensive walls; these corners were called salients. A gun firing through a slot in the wall was firing through an embrasure. A gun firing through an embrasure may or may not be on a platform, depending on the height of the wall. If a platform was used, it would not be as high, relative to the wall, as a barbette. Differing tactical considerations determined the choice between the two types of gun position. The barbette gave the gun a wide field of fire, but exposed the gun and its crew to enemy fire, while the embrasure protected the gun and its crew, but limited the field of fire and weakened the parapet.

General rules were accepted for the construction of these gun positions. A barbette was built about 20 ft deep to allow for gun recoil, regardless of the size of the gun, and spaced 15 ft apart for each gun in the position. A platform for several guns was built in multiples of the 15-x-20-ft unit. Salient barbettes, because of the diagonal position of the platform and the necessity to be able to fire the gun along any of several lines, were built in 5-x-5-ft units for single guns. Barbettes and platformed embrasured batteries had ramps about nine feet wide. The slope of the ramp was such that the length of the ramp was six times its height, so that a platform three feet high required a ramp 18 ft long. The top of the barbette was usually 2.75 ft below the top of the parapet or the mouth of the embrasure, and was covered with a plank surface to prevent the wheels of the gun carriage from cutting ruts into the earthen top of the barbette. Such ruts would prevent the carriage from rolling in recoil, which in turn would force the structure of the carriage itself to absorb the shock of firing. This would quickly smash the carriage and dismount the gun.

These rules were not hard and fast, but were guidelines which evolved from the practices of warfare of the time. Many of the terms used were French, since many of these guidelines were developed in France, and the same terms were frequently transferred virtually unchanged into both English and Spanish. Several of these French terms are used on the Sanchez-Navarro and Labastida maps, such as barbeta, for barbette, and banqueta, for banquette. The basic practices of warfare in 1835 were part of this tradition; that military engineers under General Perfecto de Cós were trained in this tradition and applied their training as best they could to the problem of the fortification of the Alamo is a reasonable assumption.

A short demonstration of the likelihood of this assumption should be included here. We know a gun platform was built in the apse of the Alamo church; through inspection of several drawings made of the walls of the apse in the 1840s, we can determine that the tops of the walls in this area of the church were virtually those visible on the interior walls of the apse today. This means the guns fired over walls