Scipio now moved southward, falling back to a position near the river Trebia, a tributary of the Po, which flows into it on its right or southern bank. Here he fortified a camp, and sat down to await the arrival of Sempronius, his colleague in the Consulship, who had been recalled from his province (Sicily) to take part in the defence of Italy. He was suffering greatly from his wound, and was unequal to the active duties of command, which, however, he was unwilling to hand over to a substitute. Probably it would have been unconstitutional to do so, when the other Consul was within reach. Yet the prætor Manlius, in whose charge the army had originally been, was probably in the camp. Constitutional forms, as we shall see again and again, weakened the military energies of Rome. Nothing could be imagined more absurd than that the army should have been entrusted to generals, changed every year, and elected by popular vote. To oppose such men to the unequalled genius of Hannibal was to ensure defeat. The mere permanence of the Carthaginian command gave him an immense advantage. But we must never forget the other side of the case. Without these constitutional forms neither Rome nor Greece (about which the historian has to say much the same thing) could have been what they were. We must expect to find in a nation as in a man the defects of its great qualities. Sempronius joined his colleague some time, it would seem, during the month of November. He was all for action. "It is intolerable," he urged, "that Italy should be invaded and Rome threatened in this fashion. And what are we waiting for? There is no third army that can join us. Our men will lose all heart if we let them sit in their camp while the enemy plunders our friends." All this is natural enough, especially when we know that the Romans had very little idea, so far, of what Hannibal really was. But Livy, doubtless, is right when he adds that Sempronius had before his eyes the approaching election of Consuls. On the 1st of January ensuing he would have to go out of office, and yield up his command. If he was to gain the distinction of a victory he must strike at once. He was encouraged by success in an affair in which he had engaged against the more prudent counsels of his colleague. He had strongly urged the duty of defending the friendly Gauls, had overruled the opposition of Scipio, and had actually carried off the honours of victory in a considerable cavalry skirmish.