Throughout history, battles have often been won not only by superior strength but by superior knowledge and deception. Sun Tzu, the ancient master of strategy, taught that all warfare is based on deception. Nowhere is this principle more vividly demonstrated than in Hannibal’s ambush of the Roman army at Lake Trasimene during the Second Punic War.
The Battle of Lake Trasimene during the Second Punic War (217 BCE) illustrates the use of deception and intelligence (or lack of) in warfare. The Carthaginian army, led by Hannibal deliberately marched through Etruria in northern Italy (modern day Tuscany) while ravaging the countryside to provoke the Romans into a rushed pursuit. Consul Gaius Flaminius, driven by emotion and lacking strategic foresight, followed Hannibal without conducting proper reconnaissance or analysis of the terrain. Hannibal lured the Roman army toward Lake Trasimene, choosing a narrow passage where the road ran between the lake and a range of wooded hills to spring his ambush. There, Hannibal carefully positioned his forces: the main force ahead to block the Roman advance, with light-armed troops and cavalry hidden in the hills to flank and attack. As the Roman column marched through the fog-covered valley at dawn, Hannibal sprang his trap. The sudden and overwhelming assault from all sides left the Roman forces no room to deploy or retreat. Flaminius was killed early in the fighting, and the Roman army was annihilated in what Polybius described as a complete and calculated ambush.[1]
Roman Consul Flaminius made a major mistake in this example, failure to gather intelligence in order to conduct a proper analysis of his situation. Flaminius did not utilize scouts to identify the lay of the land so he could conduct an analysis of the terrain or attempt to ascertain the location of enemy forces. While Flaminius failed to use the tools at his disposal, Hannibal was using deception to gain an advantage over the Roman response. That highlights the double-edged sword that is deception and intelligence. A general must use both to their advantage while also assuming the other is doing the same, creating the need to also counter the enemy’s intelligence operations and deceptions. Flaminius failed to do both.
One of Sun Tzu’s most often quoted passage is on deception saying, “Warfare is the way of deception. Thus although you are capable, display incapability to them. When committed to employing your forces, feign inactivity. When your objective is nearby, make it appear as if distant; when far away, create the illusion of being nearby.”[2] The basic principle of deception is to shape the thinking and analysis of one’s opponent- if capable, display incapability. In practice, deception means showing the enemy what the leader wants them to see in order to gain an advantage.
In order to display incapability, one can: feign retreat, send decoy units or wounded soldiers to make contact with the enemy, or hide reinforcements/elite units. By feigning retreat a general can change from one battleground to another, one that provides more advantage. Sending a decoy unit or wounded soldiers to make contact with the enemy can send the signal that an army is weakened and ripe for destruction. By hiding reinforcements or elite units an army can appear weaker than it truly is; with the goal being to induce a battle when one may have been avoided if the true strength was known.
In order to feign inactivity a general can move their forces at night or in fog (a good tactic if Flaminius had done it on purpose and used scouts); use terrain to mask movement; use decoy camps and headquarters; and minimize communication between troops. Moving forces without the enemy army detecting it is an incredibly effective way to gain an advantage. It allows an army to set up an ambush or perhaps escape from one. A decoy camp or headquarters tricks the enemy into thinking the army is located in one place when in actuality it is located somewhere else. That can also be used to set up an ambush, move to gain some advantage, or to delay contact with the enemy army altogether.
The use of smaller forces making contact with the enemy can have the same effect as a decoy- to hold an enemy force at a location of the leader’s choosing. A close force can make an enemy army hold in a location, while allowing the enemy to see a force far away can make that enemy move.
It is important to note that the above examples of deceptions can be utilized in conjunction with each other in order to gain the maximum advantage. In fact, that is likely required. For example, if a general wants to move an enemy army to a potential ambush that general must induce that army to move while hiding the true location or strength of their own force. Therefore, they may send a smaller force far away in the direction they want the enemy army to travel, ensure that force is not only seen, but also convinces the enemy leadership that it’s the entire army. All while the general utilizes terrain to move the bulk of the fighting force into position. With this constant game of deception between two forces playing out it would seem nearly impossible to ascertain an enemy’s true position and motives. That is the purpose of intelligence.
Sun Tzu says, “the means by which enlightened rulers and sagacious generals moved and conquered others…was advance knowledge.”[3] Sun Tzu opens the Art of War with the importance of a ruler or general properly analyzing a situation before committing his or her forces to field- an example of strategic level of analysis and properly conducted with intelligence. To drive this point home he also states,
“If I know our troops can attack, but do not know the enemy cannot be attacked, it is only halfway to victory. If I know the enemy can be attacked, but do not realize our troops cannot attack, it is only halfway to victory.
Knowing that the enemy can be attacked, and knowing that our army can effect the attack, but not knowing the terrain is not suitable for combat, is only halfway to victory. Thus one who truly knows the army will never be deluded when he moves, never be impoverished when initiating an action.
Thus it is said if you know them and know yourself, your victory will not be imperiled. You know heaven and know earth your victory will be complete.”[4]
Intelligence
Intelligence takes many forms. It could be information about the morale of an opposing army, the route an army intends to follow, the objectives they intend to pursue, or perhaps how a particular weapon system works. Intelligence also looks at terrain analysis and is an example of information that applies to all levels of warfare (strategic, operational, and tactical).
At the strategic level a leader must know what is between the army at its home garrison location and the strategic military (physical) objectives the general is tasked to accomplish. For example, does the army need to cross a sea? How long will the army be away from its home garrisons? Will it be able to forage for food or will it need to bring food with it? Are there any specific weapon systems required to accomplish the objective? The general needs to know the broader scope of the movement in order to determine what the army needs in order to make that movement and accomplish the objective.
At the operational level, the operational commanders use their understanding of terrain to move their forces to gain some sort of advantage over the enemy force. They may identify the optimal battlefield for the fight, attempt to conceal the force’s true strength, or conceal the force’s true location. The focus at the operational level is to maneuver forces over time and space in order to achieve an advantage over the enemy’s forces. Whereas, at the tactical level tactical leaders will us the terrain chosen for the confrontation to maximize the effectiveness of their personnel and weapon systems in the fight.
To gather information, Sun Tzu discussed five types of spies: local spies, internal spies, double agents, expendable spies, and living spies. Local spies employ people from the local district. Internal spies employ the people who hold government positions. Double agents are enemy spies that have been turned against those who sent them. Expendable spies are sent into a state to spread disinformation, who are likely to be killed once their information proves to be false. Finally, living spies are those sent to return with reports.[5]
Intelligence gathering is an artform in itself. While a deep understanding of intelligence operations is outside the scope of this project it is still worth mentioning a few things here. First, useful intelligence is not always obvious. Getting intimate knowledge of an enemy’s plans or the workings of a weapon system are huge victories, however sometimes the most innocuous or unapparent information is the key to understanding. For example, American intelligence personnel were first tipped off to the presence of the Soviet armed forces on Cuba by the sudden presence of soccer fields at military bases- Cubans prefer baseball.
Second, often spies or collection operations only pick up bits and pieces of the whole picture- picture a blind man feeling the trunk of an elephant. The art is in gathering enough pieces and understanding the enemy enough to build the big picture. That takes time.
Third, scouts are the last line of defense to bad or no intelligence gathering. Sun Tzu does not specifically link scouts with intelligence- he focuses on spies. Modern militaries should and the good ones do. Hence, Flaminius’s major failure was marching into foggy terrain perfect for an ambush without any scouts. He may not have had any intelligence on his enemy, but the use of scouts would have alerted him of the danger if they had reported on Hannibal’s presence and the terrain.
Speaking of terrain, gathering information gems about weapon systems or bugging a general’s office may get the most attention and glory, but the best analysts focus on the basics- the environment and how it affects operations. The lack of focus on the terrain was also one of Flaminius’s failures. Even if his scouts didn’t detect the presence of Hannibal’s army, a proper analysis of the terrain would have alerted him of the danger of that particular stretch of road.
The Battle of Lake Trasimene offers enduring lessons beyond a single battlefield. It reveals that without intelligence and an understanding of deception, even the strongest armies can be reduced to chaos. As Sun Tzu taught, true victory lies in knowing both oneself and one’s enemy — and shaping the environment before the first arrow is loosed. In every era, from ancient Italy to the modern digital battlespace, this lesson remains unchanged. Luckily Sun Tzu has a few things to say about the effect of the environment (terrain) on operations, which is the focus for the next chapter.
[1] Polybius, The Histories, trans. W. R. Paton (Cambridge, MA: Harvard University Press, 1922), 3.82–85.
[2] Ralph D. Sawyer, trans., The Art of War (New York: Basic Books, 1994), p. 168
[3] Ibid. 231
[4] Ibid. 215
[5] Ibid. 231-232
Strategy in Brief 
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