The road led through a narrow strip of level ground with a range of high hills on each side of it lengthwise. This defile was overlooked in front crosswise by a steep hill difficult to climb, and behind it lay the lake, between which and the hill side the passage giving access to the defile was quite narrow. Hannibal coasting the lake and passing through the defile occupied himself the hill in front, encamping on it with his Spaniards and Africans; his slingers and pikemen he brought round to the front by a detour and stationed them in an extended line under the hills to the right of the defile, and similarly taking his cavalry and the Celts round the hills on the left he placed them in a continuous line under these hills, so that the last of them were just at the entrance to the defile, lying between the hillside and the lake.
Having made all these preparations during the night and thus encompassed the defile with troops waiting in ambush, Hannibal remained quite. Flaminius was following close on his steps impatient to overtake him. He had encamped the night before at a very late hour close to the lake itself; and next day as soon as it was dawn he led his vanguard along the lake to the above-mentioned defile, with the view of coming in touch with the enemy.
Walbank Commentary