After out-manoeuvring the
Romans and learning of the approach of the headstrong Roman general, Flaminius, Hannibal set up an ambush near Lake Trasimeno to head off the pursuing army. By design, this move forced Flaminius' army into open combat, and, as it passed between the northern shore of Lake Trasimene and the opposite hills.
On the morning of June 24, 217 b.C. (according to the non-reformed calendar, and corresponding to April in the Julian calendar) Consul Flaminius ordered his troops to start again in pursuit of the Carthaginians. The night before Hannibal had instructed his men to light fires on the hills of Tuoro, so that the Romans would believe that his forces were farther away than they actually were. The truth of the matter was that his men were laid out in such way as to surround their enemies from all sides.
The Romans moved off in a thick fog, winding along the narrow valley. All at once Hannibal gave orders for a general attack. From the surrounding hills the Carthaginian cavalry and infantry came down with an enormous impact, engaging the enemy army from all sides. The Romans did not even have time to draw up in their usual battle array, and were forced to fight in open order. The Carthaginians drove them on to the lake, where there was no escape.
It was a terrible massacre: Hannibal's troops destroyed almost the entire Roman army of 25,000, killing possibly 15.000 Roman soldiers, including Consul Flaminius himself, were killed. Many were driven to drown in the lake. An ancient tradition says that because of the blood, which for over three days filled the area, the name of the stream which crosses it was changed to Sanguineto - Blood River.
Reinforcements of about 4,000 cavalry under Gaius Centenius were intercepted before they arrived and were also destroyed