He arrived in Etruria in the spring of 217 BC and decided to lure the main Roman army under Flaminius into a pitched battle by devastating the region that Flaminius had been sent to protect. As Polybius recounts, "he [Hannibal] calculated that, if he passed the camp and made a descent into the district beyond, Flaminius (partly for fear of popular reproach and partly of personal irritation) would be unable to endure watching passively the devastation of the country but would spontaneously follow him... and give him opportunities for attack." At the same time, Hannibal tried to break the allegiance of Rome's allies by proving that Flaminius was powerless to protect them. Despite this, Flaminius remained passively encamped at Arretium. Hannibal marched boldly around Flaminius' left flank, unable to draw him into battle by mere devastation, and effectively cut him off from Rome (thus executing the first recorded turning movement in military history). He then advanced through the uplands of Etruria, provoking Flaminius into a hasty pursuit and catching him in a defile on the shore of Lake Trasimenus. There Hannibal destroyed Flaminius' army in the waters or on the adjoining slopes, killing Flaminius as well (see Battle of Lake Trasimene). This was the most costly ambush that the Romans ever sustained until the Battle of Carrhae against the Parthian Empire.