The Romans accept the fight (end of December)
Between the two armies flowed a stream, enclosed on all sides in deep banks and covered with marshy grasses, bushes, brushwood, as all uncultivated places usually are. One could even hide cavalry in this dark place:Hannibal noticed it, after having recognized the terrain himself:"This will be your post, he said to Mago, his brother:choose from the army one hundred horsemen , a hundred infantry, and come with them to join me in the first watch. Now it is necessary to take food and rest." He says, and dismisses the council. Magon soon appears with his elite troop. “I see, says Hannibal, intrepid warriors. But, in order to assure you the advantage of numbers as well as of valor, you will each choose, in all the infantry or cavalry battalions, nine brave men who resemble you. Magon will show you where to lie in wait. You will be dealing with an enemy unable to see anything in these ruses of war." The thousand horsemen and the thousand infantry of Magon are gone. Hannibal, at daybreak, orders the Numidian cavalry to cross the Trebia, to hover along the Roman camp, and to harass the outposts, to draw the enemy into battle; then, when the action would be engaged, to let go little by little, in order to drag it below the river. Such were the instructions of the Numidians. The other chiefs of the infantry and the cavalry receive the order to have all their soldiers dine, then saddle the horses, and wait for the signal under arms. Sempronius, at the first alert given by the Numidians, first advances all his cavalry, that part of his forces of which he is so proud, then six thousand infantry, and finally all his troops, so eager was he to carry out his long-forgotten resolve to fight. On that day the mist was rather sharp, and snow was falling in these places situated between the Alps and the Apennines, and still cooled by the neighborhood of rivers and marshes. As the men and horses had gone out hastily, without having taken any food in advance, without having provided themselves with any protection against the rigors of the season, they had no longer any heat; and, as they approached the river, the air, becoming sharper, froze them with cold. Soon they enter the water, in order to pursue the Numidians who flee before them, and they are up to their chests, because of the rains which, the previous night, have swollen Trebia:then, as they come out of the river, they feel their limbs so numb that they can hardly hold their arms; and, as the day is already advanced, they find themselves exhausted with fatigue and need.