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                 Squat defensive bastions with acutely angled faces replaced the round, tall towers of the
medieval era. The angle of the walls of each of
these bastions was such that any other bastion along the intersecting wall could support the besieged bastion, raking fire along it with no gaps in the fields of fire. This new fortification, when viewed from above, looked like a diamond rather than a circle. The new center of defense moved from the tower to the bastion and the bastion
itself continued to develop and improve with experimentation. The shoulders of the bastions, that being the corners of the structure across the shorter diameter, morphed into a “retired flank,” making a bastion within a bastion. These positions allowed the most casualty producing firearms to rake their fire across the walls of the fortification, much like the modern concept of the Final Protective Line that Soldiers are required to indicate on their range cards. Christopher Duffy, in his book Siege Warfare summed up what trace itallienne was designed
to do, “At a tactical level a fortress was simply an arrangement of fire-swept obstacles, a prepared battlefield on which the advantages were piled up on the side of the defender.” This is the same tactical considerations taught at the very lowest levels
of our modern military. Our modern defensive doctrine has inherited more than just interlocking fields of fire from the trace itallienne. The very outline, the very trace, of modern defenses looks much like those of the late fifteenth century.
Period illustration of a trace itallienne fortification. Notice the retired flanks where the bastions meet the walls. These recesses provided better fields of fire along the walls of the fortification.
The Modern Case for the Trace Itallienne.
While engineers do not have the time or resources to build a full defensive position for
every stop a forward operating platoon takes, the principals of the trace itallienne are still practiced today, now relying on weapons’ fire rather than walls to prevent a breach into the defense’s
interior. The perimeter defense described in FM 3-21.71: Mechanized Infantry Platoon and Squad (Bradley), 5-33 looks almost identical to the bastion designs discussed earlier. The walls and bastions
are replaced with wire and Bradley vehicles in defensive positions. FM 3-21.71 calls out these specific characteristics:
• The trace of the platoon is circular or triangular rather than linear.
• Unoccupied areas between squads and vehicles are smaller.
• The flanks of squads and sections are bent back to conform to the plan.
• The bulk of combat power is on the perimeter. • The reserve is centrally located.
These concepts fall in line with the expectations of any defense in history. The FM continues that this type of defense is uncommon at the platoon level, as it lacks the task force level of support preferred for a static defense and that platoon defensive positions can rely more on mobility rather than a static defense. FM 3-21.17 does allow that sometimes a forward platoon may need the ability to provide 360-degree security when isolated by the enemy and forward of friendly positions and because of this, should be trained in the concept.
The trace itallienne has not only influenced the mechanized infantry defense but also light infantry defenses. The patrol base as described in FM 3-21.8: The Infantry Rifle Platoon and Squad, 3-151, creates a triangular trace that appears somewhat dissimilar to the trace itallienne. However, once sectors of fire are drawn over the position, the resemblance become clear. The star like patterns of the interlocking fields of fire emerge and illustrates that the light infantry patrol base still shares a heritage with its predecessors but distilled down
to what is essentially a three walled trace itallienne. The Ranger Handbook further reduces the number of strong points in a defense to that of oval while still depending on interlocking fields of fire with the cigar shaped patrol base. Here, the ends of
the cigars work as their own retired flanks and can fire along the forward edge of the patrol base.
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