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 15,000 prisoner. A cavalry force of 4,000 from the other Roman army were also engaged and wiped out. The prisoners were badly treated if they were Romans, but released if they were from one of Rome's Latin allies. Hannibal hoped some of these allies could be persuaded to defect, and marched south in the hope of winning over Roman allies among the ethnic Greek and Italic city states.