OTTO IV (c. 1182–1218)  , Roman emperor, second son of Henry the Lion, duke of Saxony, and Matilda, daughter of Henry II., king of England, was most probably born at Argenton in central France . His father died when he was still young, and he was educated at the court of his uncle Richard I., king of England, under whose leadership he gained valuable experience in war, being appointed duke of Aquitaine, count of Poitou and earl of Yorkshire . When the emperor Henry VI. died in September 1197, some of the princes under the leadership of Adolph, archbishop of Cologne, were anxious to find a rival to Philip, duke of Swabia, who had been elected German king . After some delay their choice fell upon Otto, who was chosen king at Cologne on the 9th of June 1198 . Hostilities broke out at once, and Otto, who drew his main support from his hereditary possessions in the Rhineland and Saxony, seized Aix-la-Chapelle, and was crowned there on the 12th of July 1198 . The earlier course of the war was unfavourable to Otto, whose position was weakened by the death of Richard of England in April 1199; but his cause began to improve when Pope Innocent III. declared for him and placed his rival under the ban in April 1201 . This support was purchased by a capitulation signed by Otto at Neuss, which ratified the independence and decided the boundaries of the States of the Church, and was the first authentic basis for the practical authority of the pope in central Italy . In 1200 an attack made by Philip on Brunswick was beaten off, the city of Worms was taken, and subsequently the aid of Ottakar I., king of Bohemia, was won for Otto . The papal legate Guido worked energetically on his behalf, several princes were persuaded to desert Philip and by the e..d of 1203 his success seemed assured . But after a period of reverses, Otto was wounded during a fight in July 1206 and compelled to take refuge in Cologne . Retiring to Denmark, he obtained military assistance from King Waldemar II., and a visit to England procured monetary aid from King John, after which he managed to maintain his position in Brunswick . Preparations were made to drive him from his last refuge, when he was saved by the murder of Philip in June 1208 .

Many of the supporters of Philip now made overtures to Otto, and an

attempt to set up Henry I. duke of Brabant having failed, Otto submitted to a fresh election and was chosen German king at Frankfort on the 11th of November 1208 in the presence of a large gathering of princes . A general reconciliation followed, which was assisted by the betrothal of Otto to Philip's eldest daughter Beatrix, but as she was only ten years old, the marriage was deferred until the 22nd of July 1212 . The pope who had previously recognized the victorious Philip, hastened to return to the side of Otto; the capitulation of Neuss was renewed and large concessions were made to the church . In August 1209 the king set out for Italy . Meeting with no opposition, he was received at Viterbo by Innocent, but refused the papal demand that he should concede to the church all the territories which, previous to 1197, had been in dispute between the Empire and the Papacy, consenting, however, not to claim supremacy over Sicily . He was crowned emperor at Rome on the 4th of October 1209, a ceremony which was followed by fighting between the Romans and the German soldiers . The pope then requested the emperor to leave Roman territory;but he remained near Rome for some days, demanding satisfaction for the losses suffered by his troops . The breach with Innocent soon widened, and in violation of the treaty made with the pope Otto attempted to recover for the Empire all the property which Innocent had annexed to the Church, and rewarded his supporters with large estates in the disputed territories . Having occupied Tuscany he marched into Apulia, part of the kingdom of Frederick of Hohenstaufen, afterwards the emperor Frederick II., and on the 18th of November 1210 was excommunicated by the pope . Regardless of this sentence Otto completed the conquest of southern Italy, but the efforts of Innocent had succeeded in arousing considerable opposition in Germany, where the rebels were also supported by Philip Augustus, king of France . A number of princes assembled at Nuremberg declared Otto deposed, and invited Frederick to fill the vacant throne . Returning to Germany in March 1212, Otto made some headway against his enemies until the arrival of Frederick towards the close of the year .

The death of his wife in August 1212 had weakened his hold on the southern duchies, and he was soon confined to the

district of the lower Rhine, although supported by money from his uncle King John of England . The final blow to his fortunes came when he was decisively defeated by the French at Bouvines in Jttly 1214 . He escaped with difficulty from the fight and took refuge in Cologne . His former supporters hastened to recognize Frederick; and in 1216 he left Cologne for Brunswick, which he had received in 1202 by arrangement with his elder brother Henry . The conquest of Hamburg by the Danes, and the death of John of England, were further blows to his cause . On the 19th of May 1218 he died at the Harzburg after being loosed from the ban by a Cistercian monk, and was buried in the church of St Blasius at Brunswick . He married for his second wife in May 1214 Marie, daughter of Henry I., duke of Brabant, but left no children . See Regesta imperii V., edited by J . Ficker (Innsbruck, 1881); L. von Ranke, Weltgeschichte, Part viii . (Leipzig, 1887–1888) ; W. von Giesebrecht, Geschichte der deutschen Kaiserzeit, Band v . (Leipzig, 1888); O . Abel, Kaiser Otto IV. and Konig Friedrich II .

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Berlin, 1856); E . Winkelmann, Philipp von Schwaben and Otto IV. von Braunschweig (Leipzig, 1873-1878) ; G . Langerfeldt, Kaiser Otto der Vierte (Hanover, 1872); R . Schwemer, Innocenz III. and die deutsche Kirche withrend des Thronstreites (Strassburg, 1882) ; and A . Luchaire, Innocent III., la papaute et l'empire (Paris, 1906); and Innocent III., la question d'Orient (Paris, 1906) .