|Battle of Lake Trasimene|
|Part of the Second Punic War|
|Hannibal||Gaius Flaminius †|
|50,000+ soldiers||40,000 soldiers|
|Casualties and losses|
|2,500 killed and "many" dead from wounds||15,000 killed|
The Battle of Lake Trasimene (June 24, 217 BC, April on the Julian calendar) was a Roman defeat in the Second Punic War between the Carthaginians under Hannibal and the Romans under the consul Gaius Flaminius. The battle is one of the largest and most successful ambushes in military history.
The Romans, greatly alarmed and dismayed by Tiberius Sempronius Longus’ defeat at Trebia, immediately made plans to counter the new threat from the north. Sempronius returned to Rome and the Roman Senate resolved to elect new consuls the following year in 217 B.C. The new consuls were Gnaeus Servilius Geminus and Gaius Flaminius, the latter under threat with recall from the Senate for leaving Rome without carrying out the proper rituals upon being elected consul. The Senate commissioned Servilius to replace Publius Cornelius Scipio and take command of his army, while Flaminius was appointed to lead what remained of Sempronius’s army. Since both armies had been weakened by the defeat at Trebia, four new legions were raised. These new forces, together with the remains of the former army, were divided between the two consuls. After the battles of Ticinus and Trebia, Flaminius' army turned south to prepare a defence near Rome itself. Hannibal immediately followed, but marched faster and soon passed the Roman army. Flaminius was forced to increase the speed of his march in order to bring Hannibal to battle before reaching the city. Another force under Servilius was due to join Flaminius.
Before this could happen, Hannibal lured Gaius Flaminius' force into a pitched battle, by devastating the area Flaminius had been sent to protect. Polybius wrote that Hannibal calculated that he could draw out Flaminius into battle and that "no sooner had he left the neighbourhood of Faesulae, and, advancing a short way beyond the Roman camp, made a raid upon the neighbouring country, then Flaminius became excited, and enraged at the idea that he was despised by the enemy: and as the devastation of the country went on, and he saw from the smoke that rose in every direction that the work of destruction was proceeding, he could not patiently endure the sight." At the same time, Hannibal tried to sever the allegiance of Rome’s allies, by proving that the Republic was powerless to protect them. However, Flaminius remained passively encamped at Arretium. Unable to goad Flaminius into battle, Hannibal marched boldly around his opponent’s left flank and effectively cut Flaminius off from Rome (thereby executing the earliest recorded deliberate turning movement in military history). Still, Flaminius stubbornly kept his army in camp. Hannibal decided to march on Apulia, hoping that Flaminius might follow him to a battlefield of his own choosing.
Flaminius, eager to exact revenge for the devastation of the countryside, and facing increasing political criticism from Rome, finally marched against Hannibal. Flaminius, like Sempronius, was impetuous, over-confident and lacked self-control. His advisors suggested that he send only a cavalry detachment to harass the Carthaginians and prevent them from laying waste to any more of the country, while reserving his main force until the other consul, Servilius, arrived with his army. However, it proved impossible to argue with the rash Flaminius. Livy wrote that "Though every other person in the council advised safe rather than showy measures, urging that he should wait for his colleague, in order that joining their armies, they might carry on the war with united courage and counsels ... Flaminius, in a fury ... gave out the signal for marching for battle." 
As Hannibal passed Lake Trasimene, he came to a place very suitable for an ambush, and hearing that Flaminius had broken camp and was pursuing him, made preparations for the impending battle. To the north was a series of heavily forested hills where the Malpasso Road passed along the north side of Lake Trasimene. Along the hill-bordered skirts of the lake, Hannibal camped where he was in full view of anyone entering the northern defile, and spent the night arranging his troops for battle. Below the camp, he placed his heavy infantry (Iberians, Celts, and Africans) upon a slight elevation. Here, they had ample ground from which they could charge down upon the head of the Roman column on the left flank, when it should reach the position. His cavalry and Gallic infantry were concealed in the hills in the depth of the wooded valley from which the Romans would first enter, so that they could quickly sally out and close the entrance, blocking the retreat route of the Romans. Then he posted his light troops at intervals along the height overlooking the plain, with orders to keep well hidden in the woods until signalled to attack. In addition, the night before the battle commenced, Hannibal ordered his men to light campfires on the hills of Tuoro, at a considerable distance, so as to convince the Romans that his forces were further away than they actually were.
The next morning, the Roman troops marched eastward along the road running near the northern edge of the lake. Eager for battle, Flaminius pushed his men hard and hurried up the column in the rear. Hannibal then sent a small skirmish force to draw the vanguard away from the front of the line, in order to split the Roman forces. Once all the Romans had at last marched through the foggy, narrow defile and entered the plains skirting the lake, trumpets were blown, signalling the general attack.
The Carthaginian cavalry and infantry swept down from their concealed positions in the surrounding hills, blocked the road and engaged the unsuspecting Romans from three sides. Surprised and outmanoeuvred, the Romans did not have time to draw up in battle array, and were forced to fight a desperate hand-to-hand battle in open order. The Romans were quickly split into three parts. The westernmost was attacked by the Carthaginian cavalry and forced into the lake, leaving the other two groups with no way to retreat. The centre, including Flaminius, stood its ground, but was cut down by Hannibal's Gauls after three hours of heavy combat.
In less than four hours, the Roman army was annihilated. The vanguard saw little combat and, once the disaster to their rear became obvious, hacked their way through the skirmishers and out of the forest. Of the initial Roman force of about 30,000, about 15,000 were either killed in battle or drowned while trying to escape into the lake (including Flaminius himself who was slain by the Gaul, Ducarius). Another 10,000 are reported to have made their way back to Rome by various means, and the rest were captured.. Hannibal's losses were 2,500, plus "many" who died of their wounds. About 6,000 Romans escaped, under the cover of fog, only to be captured by Maharbal the following day. Both Livy and Polybius wrote that Maharbal promised safe passage ("with a garment apiece") if they surrendered their weapons and armour, but Hannibal had them sold into slavery irrespective of the promise made.
The disaster for Rome did not end there. Within a day or two, a reinforcement force of 4,000 under the propraetor Gaius Centennius was intercepted and destroyed.
Hannibal, emerging from another brilliant victory, had successfully planned and executed the greatest ambush in history. News of the defeat caused a panic in Rome. Quintus Fabius Maximus was elected dictator by the Roman Assembly and adopted the "Fabian strategy" of avoiding pitched conflict, relying instead on low-level harassment to wear the invader down, until Rome could rebuild its military strength. Hannibal was left largely free to ravage Apulia for the next year, until the Romans ended the dictatorship and elected Paullus and Varro as consuls. The result would be the Battle of Cannae, the worst defeat the Romans would suffer throughout the Second Punic War.