Next spring the Romans positioned two armies, one on each side of the Apennines. The Carthaginians crossed the mountains by a difficult but unguarded route and so surprised the Romans. The Carthaginians moved south into Etruria, plundering, razing the villages and small towns and killing all adult males encountered. Flaminius, in charge of the nearest Roman army, set off in pursuit. Hannibal arranged an ambush on the north shore of Lake Trasimene and trapped the Romans; killing or capturing all 25,000 of them. Several days later the Carthaginians wiped out the entire cavalry contingent of the other Roman army. The ambush and destruction of one army by another is widely considered a unique occurrence.