Otto immediately set to work. He recovered for the Empire all the lands of Central Italy which Innocent had already annexed to the papal dominions, including, of course, the Matildan inheritance; he made the Roman Prefect an imperial officer again; and entering into alliance with the German followers of Henry VI, who had never been entirely dislodged from the southern kingdom, he overran Apulia and prepared, by the aid of a fleet lent by Pisa, to pass over into Sicily. Innocent did everything in his power to check the conqueror. He excommunicated him (August, 1210); in conjunction with Philip Augustus of France, the old ally of Henry VI, he roused disaffection against Otto among the German nobles. Innocent was somewhat taken aback when Otto's subjects, finding that the Pope in his anathema had absolved them from their fealty to the King, held Otto as deposed, and proceeded to elect in his place the young Frederick Roger, Henry VI's son and the papal ward, who was already King of Sicily. This choice also threatened to produce that very union of Germany and Italy which Otto was bent on accomplishing. But the need of checking Otto forced Innocent to acquiesce, and Frederick did everything to allay the papal fears. [Sidenote: Innocent and Frederick.] Since Frederick could not stop Otto's progress in the south, it was arranged that he should go north to Germany in the hope of drawing Otto away. Before he left, Frederick had his young child Henry crowned, as an earnest that he did not intend to join the kingdom he was going to seek with that which he already held. He passed through Rome on his way north, and Innocent obtained from him a repetition of his liege homage for Sicily and a promise that the two kingdoms should be kept separate. In return Innocent gave him the title of "Emperor elect by the grace of God and of the Pope," and supplied him with money. Innocent thus hoped that he had taken every precaution to avoid the dangers which he feared, while Frederick, young and inexperienced, seems to have accepted the conditions willingly and to have intended to keep them. His ambition and the unexpected prospects thus opened to him led him on regardless of consequences. [Sidenote: Otto's failure.]