He halted his troops at Cortona.

The road by which he had passed wound along the shore of Lake Trasimene, at the foot of a range of steep hills, which approached closely to the water.
Half way along these hills a stream runs down a valley into the lake, and in the valley, completely hidden from the sight of an enemy approaching, Hannibal placed the Numidian cavalry and the Gaulish infantry.

Among some woods clothing the lower slope of the hills facing the lake he placed his light troops, while the Spanish and African infantry and the Gaulish cavalry were similarly hidden on the outer slopes of the hill in readiness to close in on the rear of the Romans when they had entered on the road between the hills and the lake.
No better position could have been chosen for a surprise.

When once the Romans had entered the path between the hills and the lake there was no escape for them.

They were shut up between the wood clad hills swarming with the Carthaginian light troops and the lake, while the heavy infantry and cavalry of Hannibal were ready to fall on them front and rear.
When Flaminius arrived at Cortona late at night he heard of the ravages and executions committed by the Carthaginians, as they had passed through early in the morning, and resolved to press forward at daybreak in hopes of finding some opportunity for falling upon and punishing them.