 Hannibal's victory over the Roman army at Lake Trasimene remains, in terms of the number of men involved, the largest ambush in military history.In the prelude to the battle, Hannibal also achieved the earliest known example of a strategic turning movement.The Romans, greatly alarmed and dismayed by Tiberius Sempronius Longus's defeat at Trebia, immediately made plans to counter the new threat from the north.