It was the custom that when the two Consuls were with the army they should exercise the command on alternate days. At early dawn on his day of command Varro gave orders to the force encamped on the north bank of the Aufidus to cross the stream. This done he drew out his whole force in a long line fronting the south. He had in all about 80,000 infantry and 6,000 horse. The Roman cavalry he posted on the right wing along the river bank; the right centre consisted of the Roman foot, which was drawn up in deeper and closer formation than usual; the left centre and the left wing were made up of the horse and foot of the allies. The archers and light-armed generally were in advance of the main line. Hannibal posted his Gallic and Spanish cavalry on his left wing, _i.e._, opposite the Roman horse, and his African horse on the right. Next the mounted troops on either side was a body of African infantry, equipped with armour and weapons collected from the spoils of Trebia and Trasumennus. The centre consisted of Gauls and Spaniards. Livy speaks of the imposing effect of their stature, for physically these Celtic warriors were greatly superior to their Italian antagonists, and of their general appearance. The Gauls were naked to the waist, the Spaniards clad in linen vests, of dazzling whiteness, edged with purple. In numbers Hannibal was greatly inferior, having only 40,000 infantry. For this disadvantage he was partly compensated by the superiority of his cavalry, both in numbers and efficiency. Of this arm he had no less than 10,000. Livy tells us, though Polybius does not mention the circumstance, that a strong wind from the S.E., locally known as the Volturnus, carrying with it clouds of sand, blew into the faces of the Romans, and greatly incommoded them. The battle began, as usual, with some indecisive skirmishing between the light-armed troops on either side. The Gallic and Spanish cavalry, on the contrary, soon achieved a very decided success. There was little room for the display of tactics or even for a charge. The combatants came to close quarters, and here the great personal strength of the Celts gave them an advantage. They dismounted and dragged their antagonists from their horses. A valiant resistance was made; it was not till many had been slain in this fierce struggle that any sought safety in flight.