In early spring 217BC, the Carthaginians crossed the Apennines unopposed, taking a difficult but unguarded route. Hannibal attempted without success to draw the main Roman army under Gaius Flaminius into a pitched battle by devastating the area they had been sent to protect. Hannibal then cut off the Roman army from Rome, which provoked Flaminius into a hasty pursuit without proper reconnaissance. Hannibal set an ambush and in the Battle of Lake Trasimene completely defeated the Roman army, killing 15,000 Romans, including Flaminius, and taking 10,000 prisoners. A cavalry force of 4,000 from the other Roman army was also engaged and wiped out.