Lothair busied himself greatly with the revival of religion in his rude Saxon duchy, and with the extension of Christianity and German political influence amidst the heathens and half-heathens beyond the limits of his Empire. Side by side with the soldiers of Albert the Bear, Margrave of the North Mark, went the Christian missionaries and revivalists. At the bidding of the Emperor, Norbert left Prémontré, and became Archbishop of Magdeburg, and founded there a new house that became the second great centre of Premonstratensian ideas. Through his influence secular canons were removed from most of the cathedrals of eastern Saxony and the Marches, and replaced by Premonstratensians. Norbert wished to make Magdeburg the centre of missions to the East and a patriarchate over Polish and Wendish Christianity. New bishoprics were founded in Poland and half-heathen Pomerania, and the Polish Archbishop of Gnesen lost for a time his metropolitical power. For a time the ideas of Adalbert of Bremen were again in the ascendant, and the Pope restored the rights of Bremen over Lund and the churches of Scandinavia. From Bremen Vicelin brought Christianity to the conquered Wagrians and Abotrites. The fortress of Siegburg, built by Lothair on the Trave, both assured his supremacy and protected the famous monastery that grew up at its walls. [Sidenote: Lothair and Italy.] The alliance between Lothair and the Papacy did not involve the abdication of any imperial rights in Italy, but the pressure of German affairs put Italy somewhat in the background. A great series of changes was now being brought about in Italy. In the north and centre the communal revolution was, as we shall soon see, in full progress. In the south the Norman power was being consolidated, while a fresh schism soon distracted the Papacy. [Sidenote: Union of Sicily and Apulia by Roger, Roger II., 1127.]