Popes and Emperors 439 But the most noteworthy of Otto's acts was his interference in Italian affairs, which led to his winning for the German kings the imperial crown that Charlemagne had worn. We have seen how Charlemagne's successors divided up his realms into three parts by the Treaty of Mersen in 870 (see above, p. 382). One of these parts was the kingdom of Italy. We know but little . of what went on in Italy for some time after the Treaty of Mersen. There was incessant warfare, and the disorder was increased by the attacks of the Mohammedans. Various power- ful nobles were able to win the crown for short periods. Three at least of these Italian kings were crowned Emperor by the Pope. Then for a generation there was no Emperor in the west, until Otto the Great again secured the title. It would seem as if Otto had quite enough trouble at home, Otto the but he thought that it would make him and his reign more comes king of glorious if he added northern Italy to his realms. So in 951 Italy and he crossed the Alps, married the widow of one of the Italian crowned kings, and, without being formally crowned, was generally ac- knowledged as king of Italy. He had to hasten back to Ger- many to put down a revolt organized by his own son, but ten years later he was called to Rome by the Pope to protect him from the attacks of his enemies. Otto accepted the invitation, and the grateful Pope in return crowned him Emperor, as Charlemagne's successor (962). The coronation of Otto was a very important event in Ger- man history ; for, from this time on, the German kings, instead of confining their attention to keeping their own kingdom in order, were constantly distracted by the necessity of keeping hold on their Italian kingdom, which lay on the other side of a great range of mountains. Worse than that, they felt that they must see to it that a Pope friendly to them was elected, and this greatly added to their troubles. The succeeding German emperors had usually to make sev- eral costly and troublesome journeys to Rome, — a first one to be crowned, and then others either to depose a hostile Pope or Emperor, 962
