Similar messages had been sent to all the Gaulish tribes friendly to Carthage, and early in March Hannibal prepared to cross the Apennines and to advance against Rome.
The position occupied by the two Roman armies barred the only two roads by which it was believed that Hannibal could march upon Rome, but as soon as the spring commenced Hannibal started by a path, hitherto untrodden by troops, across the Apennines.

In the march the troops suffered even greater hardships than those which they had undergone in the passage of the Alps, for during four days and three nights they marched knee deep in water, unable for a single moment to lie down.
While ever moving backwards and forwards among his men to encourage them with his presence and words, even the iron frame of Hannibal gave way under the terrible hardships.

The long continued strain, the want of sleep, and the obnoxious miasma from the marshes, brought on a fever and cost him the sight of one of his eyes.

Of all the elephants but one survived the march, and it was with an army as worn out and exhausted as that which had issued from the Alps that he descended into the fertile plains of Tuscany, near Fiesole.
The army of Flaminius, 30,000 strong, was still lying at Arezzo, on his direct road south, and it was with this only that Hannibal had now to deal, the force of Servilius being still far away at Rimini.

His own army was some 35,000 strong, and crossing the Upper Arno near Florence, Hannibal marched towards Arezzo.