Therefore, in the spring of 217 B.C. he marched southwards, placing the Spaniards and Libyans in front, with the baggage and stores behind them, the Gauls, whom he never quite trusted, in the centre, and the Numidian light horse and cavalry in the rear, under his brother Mago. There were no elephants to be thought of now, for they had all died of cold after the battle of Trebia. North of the Arno was a wide tract of marshland, which had to be crossed before the Apennine mountains could be reached. Never, during all his campaigns, did Hannibal's army have to undergo such suffering. In many ways it was worse than the passage of the Alps, for once in the midst of the morasses, swollen by the melting snows, it was hardly possible to snatch a moment of sleep. Many of the oxen fell and died, and when this happened the wearied men stretched themselves on their still warm bodies, and closed their eyes for a short space. At length, after three nights and four days of incessant marching, till the troops were nearly numb with cold, firm ground was reached, and for a while they rested in peace on the hill of Fiesole, above the Arno. Here Hannibal formed his plans for the next campaign. He found out that Flaminius the consul was a vain, self-confident man, with neither experience nor skill in war. It would be easy, he thought, by laying waste the rich country to the south, to draw the Roman general from his camp at Arretium; and so it proved. Flaminius, greedy of glory he could never gain, refused to listen to the advice of his officers and wait for the arrival of the other consul, and set out in pursuit of Hannibal, who felt that victory was once more in his hands. The place which Hannibal chose for his battle was close to lake Thrasymene, a reedy basin in the mountains not far from the city of Cortona. At this spot a narrow valley ran down to the lake, with lines of hills on both sides, and a very steep mountain at the opposite end of the lake. At the lake end the hills came so close together that there was only a small track through which a few men could pass at a time. Making sure that his enemy was following in his footsteps, Hannibal placed his steady heavy armed Spaniards and Libyans on the hill at the end of the valley opposite the lake, in full view of anyone who might approach them. His Balearic slingers and archers, and light-armed troops, were hidden behind the rocks of the hills on the right, and the Gauls and cavalry were posted in gorges on the left, close to the entrance of the defile, but concealed by folds in the ground. Next day Flaminius arrived at the lake, and, as Hannibal intended, perceived the camp on the hill opposite. It was too late to attack that night, but the next morning, in a thick mist, the consul gave orders for the advance through the pass. Grimly smiling at the success of his scheme, Hannibal waited till the Romans were quite close to him, and then gave the signal for the assault from all three sides at once.