Otho left Rome on the 14th. of March, moving northwards to encounter the armies of Vitellius, which had already crossed the Alps. His prospects were fairly hopeful. His own forces were indeed scarcely a match for the armies of the Rhine which had descended almost en masse  into Italy; but the legions from the provinces east of the Adriatic were on their march to join him, and his fleet commanded the sea.

The opening operations of the campaign were decided in his favour. Placentia was defended with brilliant success by Spurinna, and Cæcina, one of the hostile generals, suffered a severe check, which might have been turned, but for the inaction of Otho's lieutenant, into a disastrous defeat. But after this everything went wrong. Otho had the best military skill in the Empire at his disposal, but he refused to avail himself of it. Suetonius Paulinus, who had won by his British campaigns a reputation superior to that of any of his contemporaries, was strongly against giving battle. He represented to Otho that the forces then at his disposal were inferior to the invaders', but that every day would add to his strength and diminish that of his opponent. The latter had brought their whole forces into the field. They had no reserves with which to make good any losses in battle or by sickness. From the latter cause they would without doubt suffer severely. Levies from the north would inevitably be decimated by the heat of the Italian plains as the summer advanced. He advised the Emperor to await his enemy behind the walls of the great fortified towns of Italy. Otho was too impatient to listen to these counsels. He could not bear the suspense of a protracted campaign, and so resolved to put his fortune to the touch at once. Even then the struggle might have ended in his favour, but for the fatal advice which his incompetent advisers, his brother being foremost among them, urged upon him, that he should retire to a safe distance from the scene of the action. Paulinus and his colleagues saw the folly of this proceeding, but did not venture to oppose it, fearing to be accused of risking the Emperor's life.

Otho accordingly retired to Brixellum. Two disastrous results followed. The army was weakened, for a strong force, including some of the best troops in the army, was detached to serve as an escort to the Emperor. The disparity in numbers thus became more marked than ever. What was far worse was the fact that the men lost their enthusiasm and spirit. Otho, strange to say, considering how little he showed of the soldierly temper and habit of life, was highly popular with the men, who would have fought under his eagle with an energy which they were not likely to exhibit under any other commander.

The details of the battle, as given by Tacitus, enable us to form but little idea of what actually took place. That the struggle began with a repulse of the Vitellianist cavalry we know; after that we find little that is definite, only a strong general impression, that the army of Otho was very badly commanded. We read too of one of those strange misunderstandings which have sometimes contributed to, if they have not decided, the issue of battles. A rumour went about the Othonianist legions that their adversaries had capitulated. They greeted the opposing lines with a friendly salutation and only found out their mistake from the angry response with which they were met. So far not much harm would have followed; but the proceeding suggested treachery to their own side whom the report had not reached, and could only suppose that their comrades were fraternising with the enemy. The battle raged most fiercely on the causeway of one of the great roads that ran across the Lombard plain, and on the open space between this and the Po, where a desperate conflict is recorded as having taken place between the Twenty-first Legion, a veteran corps of high reputation which had come from the camp of the Upper Rhine, and a newly levied force, the First Marine Legion, which had never yet fought in a pitched battle. In the first conflict the veterans lost their eagle; infuriated by this disgrace they returned to the charge, and drove their opponents headlong before them. Another legion from the German frontier, the Fifth, routed the Thirteenth; a portion of the Fourteenth was surrounded by superior numbers, and apparently was compelled to surrender. The Praetorians, the best troops in Otho's army, seem to have held their own, refusing afterwards to allow that they had been defeated.

Otho, meanwhile, was awaiting calmly at Brixellum the news of the result, calmly because he had made up his mind how he should act. If the victory was his, well; if not, he was determined not to fight again. He had risked everything on the issue of the day, and he was resolved to abide by it. Suetonius, the historian of the Caesars, gives us an interesting reminiscence which he had heard from his own father, an officer in one of the defeated legions. Otho had always felt the greatest horror of civil war; if his own conduct towards Galba seemed inconsistent, he excused it by having his own convictions partly justified by the result, that in this case the transference of power could be effected without a struggle. The troops seem to have been aware of the Emperor's reluctance to continue the struggle. Anyhow they at once set themselves to at once combat the resolve. They implored him not to give up hope; he had, they said, great forces still at his disposal. The Praetorians were substantially unbroken, and the legions from Moesia and from the trans-Adriatic provinces were near at hand. Indeed they had sent messengers in advance to announce their approach. These representations were undoubtedly correct. The war was not yet over, if Otho had chosen to carry it on. He had the means of prolonging the struggle, and it might have ended in his favor. But to prolong it was exactly what he had resolved not to do.

The speech in which he announced this determination is finely expressed, though how much is the historian's, how much Otho's we cannot determine. "I do not put so much value on my life, as to make me willing to expose to further danger a spirit so noble, a courage so dauntless as yours. The greater the hope you hold out to me, the more meritorious will be my death. Vitellius began this civil strife; I will at least have the credit of limiting it to a single battle. Others will have held power longer than I have done, but no one shall have left it with more distinction. I am determined that the best youth of Rome, the bravest armies of the Empire shall not be lost to it. I am content to know that you were willing to die for me." He then took farewell of his friends, and gave them such facilities as he could for leaving the place; he destroyed all documents and letters that were likely to compromise their writers. He had originally intended to kill himself that same evening, but changed his mind, playfully saying to his attendants: "I may as well live one night more." He had already discharged, as he thought, all the duties of life, leaving nothing but the preparation for death, when he was roused by a disturbance among the infuriated soldiery. They took it ill that any of the Emperor's friends should leave him and threatened with violence all who attempted to quit the town.

Verginius, a distinguished officer, who had himself refused the throne when it was offered him by the legions, was in imminent danger, the troops having besieged him in his house. Otho quieted the tumult, and waited till all who wished to go had departed in safety. At sunset, after quenching his thirst with a draught of cold water, he retired to rest, having first put a dagger under his pillow. Two had been brought to him, and he had chosen the one which had the keenest edge.

The night passed quietly. It was believed that he slept. At early dawn the freedmen who were in attendance, and who were watching for every sound, heard him groan. They hurried into his chamber, Plotius Funius, the Prefect of the Praetorians, being with them. They found Otho dead. One blow, which must have been delivered with no common firmness, had been sufficient. The last rites were hastily performed. He had been urgent in his entreaties that his remains should be at once placed on the funeral pile, dreading that his head might be cut off and made the object of insult by the conquerors. The Praetorians carried his corpse to the place where it was to be consumed, covering his hands and his wounded breast with kisses as they went. Those who could not reach the body for the crowd, showed their grief and their affection by their gestures. Soldiers who had been deputed to light the funeral pile killed themselves after they had discharged this mournful office. The number of those who committed suicide either then or shortly afterwards was surprisingly great. There was something in the man which attracted affection in a remarkable way. He had not, so far as we can make out, a single virtue beyond courage; he was vicious; unscrupulous, a foolish profligate and fop; and yet a passionate devotion, which men infinitely better than he could not raise, was lavished upon him. The cause was doubtless some personal charm which defied description.