TRASIMENUS, LAKE, a lake of Umbria, Italy, 12m. W. from Perugia, 843ft. above sea-level, 5om. in circumference, and 8m. to 14m. across (Lat. Trasumenus Lacus; Ital. Lago Trasi meno). Having no natural outlet, it was formerly subject to sudden rises, which occasioned inundations, and these in turn malaria. An artificial outlet was completed in 1898 from the south-east corner of the lake to the Caina, a small tributary of the Tiber. The locality was the scene of the second great defeat suffered by the Romans during the Second Punic War.
In the early spring of 217 B.C. Hannibal left the winter quar ters (probably near Modena or Bologna) to which he had with drawn after the victory of the Trebia (q.v.) and crossed the Apennines, continuing his march by a shorter route than the usual one, a route which obliged him to march through an inun dated and marshy district for four days and three nights. Which pass it was that he took has been much discussed, but it is most likely that he followed the modern route from Bologna to Bagni della Porretta, and thence went by the Collina pass to Pistoia. From here he passed through the (at that time) marshy district between Pistoia and Florence, and after resting his troops ad vanced towards Cortona and Lake Trasimenus, his object in tak ing this route being, as Polybius tells us, to move onto the rear of the consul Flaminius, who was at Arretium (Arezzo) and, by this strategic surprise, gain an opportunity to fight with the advantage. Fulfilling Hannibal's calculation, Flaminius, on hearing that Han nibal was plundering the countryside, hastily started in pursuit; while the other consul Servilius, who was at Ariminum, marched along the Via Flaminia, their object doubtless being to attack him from two sides before he could reach Foligno. But Flaminius advanced rapidly and without taking the most elementary pre cautions of scouting. He probably reached the lake in a single day's march from Arezzo, in any case late in the evening, and encamped by it, probably to the east of Monte Gualandro and west of Tuoro, and started early on the following morning along the north side of the lake, which was covered with a thick mist.
Hannibal, as he marched along the shores of the lake, had not failed to notice the exceptionally good opportunities of surprise which the terrain afforded. From the hill of Montigeto, a little to the west of Passignano, to Torricella, where the road to Perugia and Foligno leaves the lake and climbs some 3ooft. in
half a mile to the pass of Montecolognola over the hills which surround it, is a distance of some six or seven miles. For the greater part of this the road runs along a narrow level strip of ground completely commanded by the hills which rise from the lake, while the ascent to the pass is shut in by hills in front and on each side, with the lake behind; so that it corresponds ex tremely well with the description of Polybius. Even without the mist, which was of course an added advantage, Hannibal would have been able to conceal the greater part of his troops behind hills or in dead ground at a comparatively short distance away from the road. Flaminius, on the other hand, was in an excep tionally unfavourable situation for resistance ; there were three points at least at which his army of some 30,00o men (which, marching in column, would have formed a length of some ten m.) could be easily split up by an attack; the narrow strip of land along the shores of the lake afforded them no room for retreat nor to rally, and there was no point where they could easily break through to the north.
Hannibal therefore encamped on the pass, from which he could command a view of the defile as far back as Passignano, and kept his heavy Spanish and African troops under his own com mand to hold the pass, while the light troops were placed on the left, behind Montecolognola itself, and the Gauls and cavalry formed the right wing, which extended along the hills above the lake as far as Montigeto, the cavalry being placed at the begin ning of the defile, and concealed behind the hill of Montigeto, so as to be able to close the defile as soon as the last units of Flaminius' army had entered it. So the Romans marched on to their doom; and when the head of their column came into con tact with the troops in the centre at the pass of Montecolognola, concealment was neither possible, nor indeed necessary, and Hannibal gave the signal for a general attack. The greater part of the army was already in the trap and was attacked on all sides from the higher ground, so that, we are told, the centurions and tribunes could not even understand the situation, still less do anything to help it, and the Romans were mostly slain in their marching formation, without having any opportunity of defend ing themselves, or realizing what was to be done. Many of them were driven into the lake and met their death there.