The Battle of Lake Trasimene was a major battle in the Second Punic War. Hannibal commanding the Carthaginians decisively defeated the Romans under the consul Gaius Flaminius. The battle is one of the largest and most successful ambushes in military history.

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.

When the Romans were lured into position, 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 outmaneuvered, 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, fought 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.