After Hannibal's victory at Trebbia and in the following spring's campaign season, the Romans appointed a new command for the Consul Flaminius. Flaminius was brash and eager to meet the Carthaginian force and exact revenge for previous Roman losses. Hannibal, always the tactician, was well aware of the Roman commander's strategy and laid in wait. Initially out-maneuvering his Roman adversaries, Hannibal looked for another spot to unleash a trap. He found a perfect one at Lake Trasimenus in April of 217 BC.
Hannibal set up an ambush that would force the Romans into open terrain, sandwiched between the northern shore of the lake and the opposite hilly ground. A Carthaginian decoy baited the Romans into following it into the trap, while the bulk of the main army occupied the high ground surrounding the northern lake shores. The night before the battle commenced, Hannibal ordered his men to light camp fires on the hills of Tuoro, at a considerable distance, to give the impression that his army was much farther away. Flaminius fell for the ploy and walked through a long, foggy and narrow valley directly into the open land designed for the Carthaginian trap.
Early in the morning, Hannibal ordered a full assault on Flaminius, and the result was a complete massacre. Cavalry and infantry poured down from the hills into the unsuspecting Roman lines and caught them completely outside of their normal formations. Forced to fight in the open without the tightly formed legionary tactics, the Romans were driven against the lake and completely surrounded. In the end, the Roman army of 25,000 lost as many as 15,000 including Flaminius himself. 4,000 cavalry reinforcements, sent late under Gaius Centenius, were also intercepted and finished off in the complete Carthaginian rout. The ancients claimed that the blood was so thick in the Lake, that the name of a small stream feeding it was renamed Sanguineto, the Blood River.
When the news reached Rome, depression and fear reigned supreme. Hannibal had inflicted the worse loss in Roman history on Flaminius and their manpower resources were quickly being depleted. Hannibal's strategy of encouraging revolt among the Roman allies could have been devastating if Rome couldn't field any more legions. To counteract Hannibal's methods, the Romans elected Fabius Maximus as dictator. In times of dire need, dictatorial power allowed a single man to develop strategies, make appointments and prepare the armies without the usual political wrangling. Maximus, too, proved a brilliant choice, as his strategy of survival vs. direct combat would prove its worth, despite the unpopularity.
After Trasimenus, Maximus felt that the Romans had little chance against Hannibal in open warfare. His tactics of delay and harassment did just enough to keep the Roman allies of central Italy from switching sides to Hannibal. While Hannibal plundered and looted as he marched around the plains, he was unable to convince to people to rise with him. His generals, and his army, boosted by victory and with dreams of the ultimate prize, encouraged a direct siege on Rome itself to end the war. Hannibal, however, was well aware that despite his superior skill on the battlefield, he lacked the numbers to successfully engage in a long term siege. Siege equipment was in short supply as well, and he looked for better options for his force. Instead of moving directly on an open path to Rome, Hannibal turned south towards what he hoped would be better success among the people to join his cause.
Fabius Maximus, meanwhile, despite his efforts and success in keeping the economic and political stability of Rome at the status quo, was losing popularity among the Senate and the people. Romans wanted military success on the battlefield, not in a war of attrition. Maximus' efforts to dwindle Hannibal's army, well aware of his problems in getting reinforcements, and wait for the right moment to strike were unappreciated by a nervous and anxious population. The "Delayer" as Maximus was known, became a hated target and his dictatorship didn't last long.
Hannibal crossed the Apennines and spent the summer of 217 scouring southern Italy. He invaded Picenum, Apulia and Campania, where his tactics of divide and conquer were beginning to bear more fruit. Success in the south initiated a change within Rome. The people removed Fabius Maximus from his dictatorship and returned to the Consular elections. Gaius Terentius Varro and Lucius Aemilius Paullus were elected in his place and it was their mission to remove Hannibal for good. While the Carthaginians wintered in Gerontium, between 217 and 216 BC, the two new consuls raised a substantial army to deal with Hannibal once and for all.
In the Spring of 216 BC, Hannibal broke his winter camp and seized the large army supply depot at Cannae on the Aufidus River in Apulia. While the ancient sources vary, Varro and Paulus led upwards of 70 to 80,000 men after Hannibal. Despite previous devastating losses, Roman tradition held that force could only be countered by force, and the large rebuilt Roman army would meet Hannibal at Cannae inAugust, 216 BC.