The Battle of Lake Trasimene was fought when a Carthaginian force under Hannibal Barca ambushed a Roman army commanded by Gaius Flaminius on 21 June 217 BC, during the Second Punic War.

Impatient with his Fabian strategy of avoiding major battles, the next year the Romans elected Lucius Paullus and Gaius Varro as consuls.

These more aggressive commanders engaged Hannibal at the Battle of Cannae in 216  BC, resulting in a third and even worse disaster for Rome; it was followed by thirteen more years of war.

[4] This expansion gained Carthage silver mines, agricultural wealth, manpower, military facilities such as shipyards and territorial depth, which encouraged it to resist future Roman demands.

[8] In 219 BC a Carthaginian army under Hannibal besieged, captured and sacked Saguntum,[9][10] which led Rome to declare war on Carthage.

[16][17] The Carthaginian army crossed the Alps in October, surmounting the difficulties of climate, terrain[14] and the guerrilla tactics of the native tribes.

[18] Hannibal arrived with 20,000 infantry, 6,000 cavalry and an unknown number of war elephants – the survivors of the 37 with which he had left Iberia[19][20] – in Cisalpine Gaul.

One was stationed at Arretium and one on the Adriatic coast; they would be able to block Hannibal's possible advance into central Italy and be well positioned to move north to operate in Cisalpine Gaul.

[34] The Gallic tribes in Cisalpine Gaul recognised the Carthaginians as the dominant force and sent plentiful supplies and many recruits to Hannibal's camp.

[35][36] In spring 217 BC, probably in early May,[37] the Carthaginians crossed the Apennines unopposed, surprising the Romans by taking a difficult but unguarded route.

The Carthaginians moved south into Etruria (modern Tuscany), plundering the countryside, looting the plentiful stocks of food, razing the villages and small towns,[38][39] and killing out of hand all adult men encountered.

[42] The modern historian Adrian Goldsworthy points out that as they passed through territory devastated by the Carthaginians, there would have been a feeling of military failure and humiliation – the army existed to protect its homeland – and that the small farmers of the legions and their landowner officers would have taken this despoliation as an intense provocation.

[43] The Romans gained the impression, possibly fostered by Hannibal, that the Carthaginians were fleeing south before them; according to the ancient historian Polybius, they anticipated an easy victory.

[44] Most male Roman citizens were liable for military service and would serve as infantry, with a better-off minority providing a cavalry component.

Approximately 1,200 of the infantry, poorer or younger men unable to afford the armour and equipment of a standard legionary, served as javelin-armed skirmishers, known as velites; they carried several javelins, which would be thrown from a distance, a short sword and a 90-centimetre (3 ft) circular shield.

[52][53] Both Iberia and Gaul provided experienced infantry: unarmoured troops who would charge ferociously, but had a reputation for breaking off if a combat was protracted.

Ancient accounts state that a thick morning mist near the lake limited visibility, but some modern historians have suggested this was either invented or exaggerated to excuse the Romans' subsequent unreadiness for battle.

As it was, with the Carthaginians attacking unexpectedly from the flank and the rear, possibly with poor visibility, there was no chance to form even a rudimentary fighting line.

The openly pro-Roman ancient historian Livy,[72] who otherwise paints a poor picture of Flaminius, recorded two centuries later that he was active and valiant in attempting to rally his army and organise a defence before being cut down by a Gaul, Ducarius.

Men attempted to swim across the lake and drowned; others waded out until the water was up to their necks and the Carthaginian cavalrymen swam their horses out to chop at their exposed heads.

Later in the day they were surrounded by pursuing Carthaginians and surrendered to a force under Maharbal on the promise of being disarmed and freed; "with a garment apiece" according to Livy.

[75] The second Roman army, originally positioned on the Adriatic coast and commanded by Gnaeus Geminus, had been marching west, intending to join up with Flaminius.

The army then marched south into Apulia,[84] in the hope of winning over some of the ethnic Greek and Italic city states of southern Italy.

Quintus Fabius Maximus Verrucosus 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 while Rome rebuilt 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 in 216 BC.

[86] These more aggressive commanders offered battle to Hannibal, who accepted and won a victory at Cannae, where some 70,000 Romans were killed or captured;[87] the modern historian Richard Miles describes this as "Rome's greatest military disaster".

[95] The historian Toni Ñaco del Hoyo describes the Battle of Lake Trasimene as one of the three "great military calamities" suffered by the Romans in the first three years of the war, the others being the Trebia and Cannae.