These provisions are characteristic of the theory of the Middle Ages according to which the civil government and the Church went hand in hand in ordering and governing the life of the people. Defection from the Church was regarded by the state as quite as serious a crime as treason against itself. While the claims of the two institutions sometimes conflicted, there was no question in the minds either of the king's officials or of the clergy that both the civil and ecclesiastical government were absolutely necessary; neither class ever dreamed that they could get along without the other. [Sidenote: Foundation of towns in northern Germany.] Before the Frankish conquest the Saxons had no towns. Now, around the seat of the bishop, or about a monastery, men began to collect and towns and cities to grow up. Of these the chief was Bremen, which is still one of the most important ports of Germany. [Sidenote: Charlemagne becomes king of the Lombards.] 30. Pippin, it will be remembered, had covenanted with the papacy to protect it from its adversaries. The king of the Lombards had taken advantage of Charlemagne's seeming preoccupation with his German affairs to attack the city of Rome again. The pope immediately demanded the aid of Charlemagne, who prepared to carry out his father's pledges. He ordered the Lombard ruler to return the cities that he had taken from the pope. Upon his refusal to do this, Charlemagne invaded Lombardy in 773 with a great army and took Pavia, the capital, after a long siege. The Lombard king was forced to become a monk, and his treasure was divided among the Frankish soldiers. Charlemagne then took the extremely important step, in 774, of having himself recognized by all the Lombard dukes and counts as king of the Lombards. [Illustration: THE EMPIRE OF CHARLEMAGNE] [Sidenote: Aquitaine and Bavaria incorporated in Charlemagne's empire.] The considerable provinces of Aquitaine and Bavaria had never formed an integral part of the Frankish realms, but had remained semi-independent under their native dukes up to the time of Charlemagne. Aquitaine, whose dukes had given Pippin much trouble, was incorporated into the Frankish state in 769. As for the Bavarians, Charlemagne felt that so long as they remained under their duke he could not rely upon them to defend the Frankish empire against the Slavs, who were constantly threatening the frontiers. So he compelled the duke of Bavaria to surrender his possessions, shut him up in a monastery, and proceeded to portion out the duchy among his counts. He thus added to his realms the district that lay between his new Saxon conquest and the Lombard kingdom. [Sidenote: Foreign policy of Charlemagne.]