Worse troubles, however, were brewing within the realm. Eberhard, Duke of the Franks (the same who had carried his brother Konrad's crown to Otto's father), had taken into his own hands the punishment of a Saxon noble, instead of referring the case to the king. The latter compelled Eberhard to pay a fine of a hundred pounds of silver, and ordered that the Frank freemen who assisted him should carry dogs in their arms to the royal castle,--a form of punishment which was then considered very disgraceful. After the order had been carried into effect, Otto received the culprits kindly and gave them rich presents; but they went home brooding revenge. Eberhard allied himself with Thankmar, Otto's own half-brother by a mother from whom Henry I. had been divorced before marrying Mathilde. Giselbert, Duke of Lorraine, Otto's brother-in-law, joined the conspiracy, and even many of the Saxon nobles, who were offended because the command of the army sent against the Wends had been given to Count Hermann, followed his example. Otto's position was very critical, and if there had been more harmony of action among the conspirators, he might have lost his throne. In the struggle which ensued, Thankmar was slain and Duke Eberhard forced to surrender. But the latter was not yet subdued. During the rebellion he had taken Otto's younger brother, Henry, prisoner; he secured the latter's confidence, tempted him with the prospect of being chosen king in case Otto was overthrown, and then sent him as his intercessor to the conqueror. [Sidenote: 939. REVOLT OF OTTO'S BROTHER, HENRY.] Thus, while Otto supposed the movement had been crushed, Eberhard, Giselbert of Lorraine and Henry, who had meantime joined the latter, were secretly preparing a new rebellion. As soon as Otto discovered the fact, he collected an army and hastened to the Rhine. He had crossed the river with only a small part of his troops, the remainder being still encamped upon the eastern bank, when Giselbert and Henry suddenly appeared with a great force. Otto at first gave himself up for lost, but determined at least to fall gallantly, he and his followers fought with such desperation that they won a signal victory. Giselbert retreated to Lorraine, whither Otto was prevented from following him by new troubles among the Saxons and the subject Wends between the Elbe and Oder.